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Square-square Root And Cube-cube Root

Class 8th Mathematics NCERT Exemplar Solution
Exercise
  1. 196 is the square of Write the correct answer from the given four options.A. 11 B.…
  2. Which of the following is a square of an even number? Write the correct answer…
  3. A number ending in 9 will have the units place of its square as Write the correct…
  4. Which of the following will have 4 at the units place? Write the correct answer…
  5. How many natural numbers lie between 5^2 and 6^2 ? Write the correct answer from…
  6. Which of the following cannot be a perfect square? Write the correct answer from…
  7. The one’s digit of the cube of 23 is Write the correct answer from the given four…
  8. A square board has an area of 144 square units. How long is each side of the…
  9. Which letter best represents the location of root 25 on a number line? arrow_0^a ,…
  10. If one member of a Pythagorean triplet is 2m, then the other two members are…
  11. The sum of successive odd numbers 1, 3, 5, 7, 9, 11, 13 and 15 is Write the…
  12. The sum of first n odd natural numbers is Write the correct answer from the given…
  13. Which of the following numbers is a perfect cube? Write the correct answer from…
  14. The hypotenuse of a right triangle with its legs of lengths 3x × 4x is Write the…
  15. The next two numbers in the number pattern 1, 4, 9, 16, 25 ……..are Write the…
  16. Which among 43^2 , 67^2 , 52^2 , 59^2 would end with digit 1? Write the correct…
  17. A perfect square can never have the following digit in its ones place. Write the…
  18. Which of the following numbers is not a perfect cube? Write the correct answer…
  19. Write the correct answer from the given four options. cube root 1000 is equal…
  20. If m is the square of a natural number n, then n is Write the correct answer from…
  21. A perfect square number having n digits where n is even will have square root…
  22. If m is the cube root of n, then n is Write the correct answer from the given…
  23. The value of root 248 + root 52 + root 144 is Write the correct answer from the…
  24. Given that root 4096 = 64, the value of root 4096 + root 40.96 is Write the…
  25. There are ………………. Perfect squares between 1 and 100. Fill in the blanks to make…
  26. There are ………………. Perfect cubes between 1 and 1000. Fill in the blanks to make…
  27. The units digit in the square of 1294 is ………… . Fill in the blanks to make the…
  28. The square of 500 will have ……………. Zeroes. Fill in the blanks to make the…
  29. There are ……………… natural numbers between n^2 and (n + 1)^2 Fill in the blanks to…
  30. The square root of 24025 will have …………… digits. Fill in the blanks to make the…
  31. The square of 5.5 is …………… Fill in the blanks to make the statements true :…
  32. The square root of 5.3 × 5.3 is ………….. . Fill in the blanks to make the…
  33. The cube of 100 will have …………. Zeroes. Fill in the blanks to make the statements…
  34. 1 m^2 = ……………… cm^2 . Fill in the blanks to make the statements true :…
  35. 1 m^3 = …………….. cm^3 . Fill in the blanks to make the statements true :…
  36. Ones digit in the cube of 38 is ……………. . Fill in the blanks to make the…
  37. The square of 0.7 is …………… . Fill in the blanks to make the statements true :…
  38. The sum of first six odd natural numbers is …………. . Fill in the blanks to make…
  39. The digit at the ones place of 57^2 is ………. . Fill in the blanks to make the…
  40. The sides of a right triangle whose hypotenuse is 17 cm are ……….. and …………. .…
  41. root 1.96 = ………… . Fill in the blanks to make the statements true :…
  42. (1.2)^3 = ……………… . Fill in the blanks to make the statements true :…
  43. The cube of an odd number is always an ………… number. Fill in the blanks to make…
  44. The cube root of a number x is denoted by ……………… . Fill in the blanks to make the…
  45. The least number by which 125 be multiplied to make it a perfect square is …………….…
  46. The least number by which 72 be multiplied to make it a perfect cube is …………….. .…
  47. The least number by which 72 be divided to make it a perfect cube is ……………. .…
  48. Cube of a number ending in 7 will end in the digit ……………….. . Fill in the blanks…
  49. The square of 86 will have 6 at the units place. State whether the statements are…
  50. The sum of two perfect squares is a perfect square. State whether the statements…
  51. The product of two perfect squares is a perfect square. State whether the…
  52. There is no square number between 50 and 60. State whether the statements are…
  53. The square root of 1521 is 31. State whether the statements are true (T) or false…
  54. Each prime factor appears 3 times in its cube. State whether the statements are…
  55. The square of 2.8 is 78.4. State whether the statements are true (T) or false…
  56. The cube of 0.4 is 0.064. State whether the statements are true (T) or false (F).…
  57. The square root of 0.9 is 0.3. State whether the statements are true (T) or false…
  58. The square of every natural number is always greater than the number itself.…
  59. The cube root of 8000 is 200. State whether the statements are true (T) or false…
  60. There are five perfect cubes between 1 and 100. State whether the statements are…
  61. There are 200 natural numbers between 100^2 and 101^2 . State whether the…
  62. The sum of first n odd natural numbers is n^2 . State whether the statements are…
  63. 1000 is a perfect square. State whether the statements are true (T) or false (F).…
  64. A perfect square can have 8 as its units digit. State whether the statements are…
  65. For every natural number m (2m-1, 2m^2 -2m,2m^2 -2m + 1) is a Pythagorean…
  66. All numbers of a Pythagorean triplet are odd. State whether the statements are…
  67. For an integer a, a^3 is always greater than a^2 . State whether the statements…
  68. If x and y are integers such that x^2 y^2 , then x^3 y^3 . State whether the…
  69. If x and y be natural numbers. If x divides y, then x^3 divides y^3 . State…
  70. If a^2 ends in 5, then a^3 ends in 25. State whether the statements are true (T)…
  71. If a^2 ends in 9, then a^3 ends in 7. State whether the statements are true (T)…
  72. The square root of a perfect square of n digits will have (n+1/2) digits, if n is…
  73. Square root of a number x is denoted by root x . State whether the statements are…
  74. A number having 7 at its ones place will have 3 at the units place of its square.…
  75. A number having 7 at its ones place will have 3 at the ones place of its cube.…
  76. The cube of a one-digit number cannot be a two digit number. State whether the…
  77. Cube of an even number is odd. State whether the statements are true (T) or false…
  78. Cube of an odd number is even. State whether the statements are true (T) or false…
  79. Cube of an even number is even. State whether the statements are true (T) or…
  80. Cube of an odd number is odd. State whether the statements are true (T) or false…
  81. 999 is a perfect cube. State whether the statements are true (T) or false (F).…
  82. 363×81 is a perfect cube. State whether the statements are true (T) or false (F).…
  83. Cube roots of 8 are + 2 and -2. State whether the statements are true (T) or…
  84. cube root 8+27 = cube root 8 + cube root 27 State whether the statements are true…
  85. There is no cube root of a negative integer. State whether the statements are…
  86. Square of a number is positive, so the cube of that number will also be positive.…
  87. Write the first five square numbers.
  88. Write cubes of first three multiples of 3.
  89. Show that 500 is not a perfect squae.
  90. Express 81 as the sum of first nine consecutive odd numbers.
  91. Using prime factorisation, find which of the following are perfect squares. (a)…
  92. Using prime factorisation, find which of the following are perfect cubes. (a) 128…
  93. Using distributive law, find the squares of (a) 101 (b) 72
  94. Can a right triangle with sides 6 cm, 10 cm and 8 cm be formed? Give reason.…
  95. Write the Pythagorean triplet whose one of the numbers is 4.
  96. Using prime factorisation, find the square roots of (a) 11025 (b) 4761…
  97. Using prime factorisation, find the cube roots of (a) 512 (b) 2197…
  98. Is 176 a perfect square? If not, find the smallest number by which it should be…
  99. Is 9720 a perfect cube? If not, find the smallest number by which it should be…
  100. Write two Pythagorean triplets each having one of the numbers as 5.…
  101. By what smallest number should 216 be divided so that the quotient is a perfect…
  102. By what smallest number should 3600 be multiplied so that the quotient is a…
  103. (a) 1369 (b) 5625 Find the square root of the following by long division method.…
  104. (a) 27.04 (b) 1.44 Find the square root of the following by long division…
  105. What is the least number that should be subtracted from 1385 to get a perfect…
  106. What is the least number that should be added to 6200 to make it a perfect…
  107. Find the least number of four digits that is a perfect square.
  108. Find the greatest number of three digits that is a perfect square.…
  109. Find the least square number which is exactly divisible by 3, 4, 5, 6, and 8.…
  110. Find the length of the side of a square if the length of its diagonal is 10 cm.…
  111. A decimal number is multiplied by itself. If the product is 51.84. find the…
  112. Find the decimal fraction which when multiplied by itself gives 84.64.…
  113. A farmer wants to plough his square field of side 150m. How much area will he…
  114. What will be the number of unit squares on each side of a square graph paper if…
  115. If one side of a cube is 15 m in length, find its volume.
  116. The dimensions of a rectangular field are 80 m and 18 m. Find the length of its…
  117. Find the area of a square field if its perimeter is 96 m.
  118. Find the length of each side of a cube if its volume is 512 cm^3 .…
  119. Three numbers are in the ratio 1 : 2 : 3 and the sum of their cubes is 4500.…
  120. How many square metres of carpet will be required for a square room of side 6.5…
  121. Find the side of a square whose area is equal to the area of a rectangle with…
  122. Difference of two perfect cubes is 189. If the cube root of the smaller of the…
  123. Find the number of plants in each row if 1024 plants are arranged so that number…
  124. A hall has a capacity of 2704 seats. If the number of rows is equal to the…
  125. A General wish to draw up his 7500 soldiers in the form of a square. After…
  126. 8649 students were sitting in a lecture room in such a manner that there were as…
  127. Rahul walks 12 m north from his house and turns west to walk 35 m to reach his…
  128. A 5.5 m long ladder is leaned against a wall. The ladder reaches the wall to a…
  129. A king wanted to reward his advisor, a wise man of the kingdom. So he asked the…
  130. Find three numbers in the ratio 2 : 3 : 5, the sum of whose squares if 608.…
  131. Find the smallest square number divisible by each one of the numbers 8, 9 and…
  132. The area of a square plot is 101 1/400 m^2 . Find the length of one side of the…
  133. Find the square root of 324 by the method of repeated substraction.…
  134. Three numbers are in the ratio 2 : 3: 4. The sum of their cubes is 0.334125.…
  135. Evaluate : cube root 27 + cube root n integrate erdection n8 + cube root n…
  136. (5^2 + (12^2)^1/2)^3 Solve:
  137. (6^2 + (8^2)^1/2)^3 Solve:
  138. A perfect square number has four digits, none of which is zero. The digits from…
  139. Put three different numbers in the circles so that when you add the numbers at…
  140. The perimeters of two squares are 40 and 96 metres respectively. Find the…
  141. A three-digit perfect square is such that if it is viewed upside down, the…
  142. 13 and 31 is a strange pair of numbers such that their squares 169 and 961 are…

Exercise
Question 1.

Write the correct answer from the given four options.

196 is the square of
A. 11

B. 12

C. 14

D. 16


Answer:

14× 14 = 196


Question 2.

Write the correct answer from the given four options.

Which of the following is a square of an even number?
A. 144 B. 169

C. 441 D. 625


Answer:

12× 12 = 144


13× 13 = 169


21× 21 = 441


25× 25 = 625


Question 3.

Write the correct answer from the given four options.

A number ending in 9 will have the units place of its square as
A. 3

B. 9

C. 1

D. 6


Answer:

If a number ends with 1 or 9 its square ends with 1.


For example- 9× 9 = 81


Question 4.

Write the correct answer from the given four options.

Which of the following will have 4 at the units place?
A. 142

B. 622

C. 272

D. 352


Answer:

If a number ends with 2 or 8 its square ends with 4.


For example- 12× 12 = 144


Question 5.

Write the correct answer from the given four options.

How many natural numbers lie between 52 and 62?
A. 9

B. 10

C. 11

D. 12


Answer:

There are 2n non-perfect square numbers between the squares of the number n and (n + 1).


Here n = 5


⇒ Natural numbers lying between 52 and 62 = 2×5 = 10


Question 6.

Write the correct answer from the given four options.

Which of the following cannot be a perfect square?
A. 841

B. 529

C. 198

D. All of the above


Answer:

No perfect square has 2, 3, 7 and 8 at its unit place.


Question 7.

Write the correct answer from the given four options.

The one’s digit of the cube of 23 is
A. 6

B. 7

C. 3

D. 9


Answer:

The ones digit of any number with 3 at its unit place is 9.


i.e. 132 = 169


Question 8.

Write the correct answer from the given four options.

A square board has an area of 144 square units. How long is each side of the board?
A. 11 units

B. 12 units

C. 13 units

D. 14 units


Answer:

Area of a square board = side × side


⇒ side = √144


⇒ side = 12 units


Question 9.

Write the correct answer from the given four options.

Which letter best represents the location of on a number line?


A. A

B. B

C. C

D. D


Answer:

∵ √25 = 5


So, C represents the location of it.


Question 10.

Write the correct answer from the given four options.

If one member of a Pythagorean triplet is 2m, then the other two members are
A. m, m2 + 1

B. m2 + 1, m2 - 1

C. m2, m2 – 1

D. m2, m + 1


Answer:

∵ (2m)2 + (m2 – 1)2 = (m2 + 1)2


Question 11.

Write the correct answer from the given four options.

The sum of successive odd numbers 1, 3, 5, 7, 9, 11, 13 and 15 is
A. 81

B. 64

C. 49

D. 36


Answer:

∵ Every square can be expressed as a sum of successive odd natural numbers from 1.


⇒ The sum of first n odd natural numbers is n2


Here, n = 8 ⇒ 1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 = 8× 8 = 64


Question 12.

Write the correct answer from the given four options.

The sum of first n odd natural numbers is
A. 2n + 1

B. n2

C. n2 - 1

D. n2 + 1


Answer:

∵ Every square can be expressed as a sum of successive odd natural numbers from 1.


⇒ The sum of first n odd natural numbers is n2


Question 13.

Write the correct answer from the given four options.

Which of the following numbers is a perfect cube?
A. 243

B. 216

C. 392

D. 8640


Answer:

9× 9× 3 = 243


6× 6× 6 = 216


8× 7× 7 = 392


8× 8× 5× 3× 3× 3 = 8640


Question 14.

Write the correct answer from the given four options.

The hypotenuse of a right triangle with its legs of lengths 3x × 4x is
A. 5x

B. 7x

C. 16x

D. 25x


Answer:

Using Pythagoras triplets: (2m)2 + (m2 – 1)2 = (m2 + 1)2


2m = 4x


⇒ m = 2


m2 – 1 = (4-1)x = 3x


⇒ m2 + 1 = (4 + 1)x = 5x


Question 15.

Write the correct answer from the given four options.

The next two numbers in the number pattern 1, 4, 9, 16, 25 ……..are
A. 35, 48

B. 36, 49

C. 36, 48

D. 35, 49


Answer:

1× 1 = 1


2× 2 = 4


3× 3 = 9


4× 4 = 16


5× 5 = 25


6× 6 = 36


7× 7 = 49


Question 16.

Write the correct answer from the given four options.

Which among 432, 672, 522, 592 would end with digit 1?
A. 432

B. 672

C. 522

D. 592


Answer:

If a number ends with 1 or 9 its square ends with 1.


For example- 9× 9 = 81


Question 17.

Write the correct answer from the given four options.

A perfect square can never have the following digit in its ones place.
A. 1

B. 8

C. 0

D. 6


Answer:

No perfect square has 2, 3, 7 and 8 at its unit place.


Question 18.

Write the correct answer from the given four options.

Which of the following numbers is not a perfect cube?
A. 216

B. 567

C. 125

D. 343


Answer:

6× 6× 6 = 216


9× 9× 7 = 567


5× 5× 5 = 125


7× 7× 7 = 343


Question 19.

Write the correct answer from the given four options.

is equal to
A. 10

B. 100

C. 1

D. None of these


Answer:

10× 10× 10 = 1000


Question 20.

Write the correct answer from the given four options.

If m is the square of a natural number n, then n is
A. the square of m

B. greater than m

C. equal to m

D.


Answer:

Given n2 = m


⇒ n = √m


Question 21.

Write the correct answer from the given four options.

A perfect square number having n digits where n is even will have square root with
A. n + 1 digit

B. digit

C. digit

D. digit


Answer:

A perfect square number having n digits where n is even will have square root with digits.


Question 22.

Write the correct answer from the given four options.

If m is the cube root of n, then n is
A. m3

B.

C.

D.


Answer:

Given


⇒ n = m3


Question 23.

Write the correct answer from the given four options.

The value of is
A. 14

B. 12

C. 16

D. 13


Answer:



Question 24.

Write the correct answer from the given four options.

Given that = 64, the value of is
A. 74

B. 60.4

C. 64.4

D. 70.4


Answer:



So,


Question 25.

Fill in the blanks to make the statements true :

There are ………………. Perfect squares between 1 and 100.


Answer:

Between 1 and 100, 81 = 92 is the highest perfect square.


Excluding 1 there are 8 perfect squares between them.


Question 26.

Fill in the blanks to make the statements true :

There are ………………. Perfect cubes between 1 and 1000.


Answer:

Between 1 and 1000, 729 = 93 is the highest perfect cube.


Excluding 1 there are 8 perfect cubes between them.


Question 27.

Fill in the blanks to make the statements true :

The units digit in the square of 1294 is ………… .


Answer:

If a number ends with 4 or 6 its square ends with 6.


Question 28.

Fill in the blanks to make the statements true :

The square of 500 will have ……………. Zeroes.


Answer:

500 × 500 = 250000


Question 29.

Fill in the blanks to make the statements true :

There are ……………… natural numbers between n2 and (n + 1)2


Answer:

There are 2n non perfect square numbers between the squares of the number n and (n + 1).


Example: n = 5


⇒ Natural numbers lying between 52 and 62 = 2×5 = 10


Question 30.

Fill in the blanks to make the statements true :

The square root of 24025 will have …………… digits.


Answer:

A perfect square number having n digits where n is odd will have square root with digits.


Here n = 5, square root will have digits


Question 31.

Fill in the blanks to make the statements true :

The square of 5.5 is ……………


Answer:

5.5× 5.5 = 55× 55× 0.1× 0.1 = 3025× 0.01 = 30.25


Question 32.

Fill in the blanks to make the statements true :

The square root of 5.3 × 5.3 is ………….. .


Answer:


Question 33.

Fill in the blanks to make the statements true :

The cube of 100 will have …………. Zeroes.


Answer:

100 × 100× 100 = 1000000


Question 34.

Fill in the blanks to make the statements true :

1 m2 = ……………… cm2.


Answer:

1 m = 100 cm


1 m2 = 100× 100 cm2 = 10000 cm2


Question 35.

Fill in the blanks to make the statements true :

1 m3 = …………….. cm3.


Answer:

1 m = 100 cm


1 m3 = 100× 100× 100 cm3 = 1000000 cm3


Question 36.

Fill in the blanks to make the statements true :

Ones digit in the cube of 38 is ……………. .


Answer:

Ones digit in the cube of 38 is 2 because for any number which lasts with 8 has 2 at its end place in cube.


For example:


8× 8× 8 = 512


Question 37.

Fill in the blanks to make the statements true :

The square of 0.7 is …………… .


Answer:

0.7× 0.7 = 7× 7× 0.1× 0.1 = 49× 0.01 = 0.49


Question 38.

Fill in the blanks to make the statements true :

The sum of first six odd natural numbers is …………. .


Answer:

∵ Every square can be expressed as a sum of successive odd natural numbers from 1.


⇒ The sum of first n odd natural numbers is n2


Here, n = 6 ⇒ 1 + 3 + 5 + 7 + 9 + 11 = 6× 6 = 36


Question 39.

Fill in the blanks to make the statements true :

The digit at the ones place of 572 is ………. .


Answer:

If a number ends with 3 or 7 its square ends with 9.


Question 40.

Fill in the blanks to make the statements true :

The sides of a right triangle whose hypotenuse is 17 cm are ……….. and …………. .


Answer:

Using Pythagoras triplets: (2m)2 + (m2 – 1)2 = (m2 + 1)2


m2 + 1 = 17


⇒ m2 = 16


⇒ m = 4


Now, m2 – 1 = (16 - 1) = 15


And 2m = 2× 4 = 8


Question 41.

Fill in the blanks to make the statements true :

= ………… .


Answer:


Question 42.

Fill in the blanks to make the statements true :

(1.2)3 = ……………… .


Answer:

1.2× 1.2× 1.2 = 12× 12× 12× 0.1× 0.1× 0.1 = 1728× 0.001 = 1.728


Question 43.

Fill in the blanks to make the statements true :

The cube of an odd number is always an ………… number.


Answer:

For example,


3× 3× 3 = 27


Question 44.

Fill in the blanks to make the statements true :

The cube root of a number x is denoted by ……………… .


Answer:

Given


Question 45.

Fill in the blanks to make the statements true :

The least number by which 125 be multiplied to make it a perfect square is ……………. .


Answer:

125 = 5×5× 5


So, 5 is the least number by which 125 be multiplied to make it a perfect square


Question 46.

Fill in the blanks to make the statements true :

The least number by which 72 be multiplied to make it a perfect cube is …………….. .


Answer:

72 = 2× 2×2× 3× 3


So, 3 is the least number by which 72 be multiplied to make it a perfect cube


Question 47.

Fill in the blanks to make the statements true :

The least number by which 72 be divided to make it a perfect cube is ……………. .


Answer:

72 = 2× 2×2× 3× 3


So, 9 is the least number by which 72 be multiplied to make it a perfect cube


Question 48.

Fill in the blanks to make the statements true :

Cube of a number ending in 7 will end in the digit ……………….. .


Answer:

If a number ends with 7 its cube ends with 3.


Question 49.

State whether the statements are true (T) or false (F).

The square of 86 will have 6 at the units place.


Answer:

Given: square of 86

We know that, the unit’s digit of the square of a number having digits 4 or 6 at unit’s place is 6.


Hence, the given statement is true.



Question 50.

State whether the statements are true (T) or false (F).

The sum of two perfect squares is a perfect square.


Answer:

Given: two perfect squares

Let us take an example:


16 and 25 both are perfect square,


But 16 + 25 = 41 which is not a perfect square.


Hence, the given statement is false.



Question 51.

State whether the statements are true (T) or false (F).

The product of two perfect squares is a perfect square.


Answer:

Given: two perfect squares

Let us take an example:


16 and 25 both are perfect square,


But 16 × 25 = 400 which is a perfect square.


Same is true for values too.


Hence, the given statement is true.



Question 52.

State whether the statements are true (T) or false (F).

There is no square number between 50 and 60.


Answer:

Given: number between 50 and 60

i.e. 51, 52, 53, 54, 55, 56, 57, 58, 59


we observe that there is no perfect square in between these.


Hence, the given statement is true.



Question 53.

State whether the statements are true (T) or false (F).

The square root of 1521 is 31.


Answer:

Given: square root of 1521

As we know,


(31)2 = 961


⇒ 1521 ≠ square root of 31


Hence, the given statement is false.



Question 54.

State whether the statements are true (T) or false (F).

Each prime factor appears 3 times in its cube.


Answer:

Given:

If a3 is the cube and m is one of the prime factor of a. Then, m appears three times in a3.


Hence, the given statement is True.



Question 55.

State whether the statements are true (T) or false (F).

The square of 2.8 is 78.4.


Answer:

Given: 2.8

As we know,


(2.8)2 = 7.84


and 7.84 ≠ 78.4


Hence, the given statement is false.



Question 56.

State whether the statements are true (T) or false (F).

The cube of 0.4 is 0.064.


Answer:

Given: 0.4

As we know,


(0.4)3 = 0.064


and 0.064 = 0.064


Hence, the given statement is True.



Question 57.

State whether the statements are true (T) or false (F).

The square root of 0.9 is 0.3.


Answer:

Given: square root of 0.9

As we know,


(0.3)2 = 0.09


⇒ 0.9 ≠ square root of 0.3


Hence, the given statement is false.



Question 58.

State whether the statements are true (T) or false (F).

The square of every natural number is always greater than the number itself.


Answer:

Given: natural number

As we know, 1 is a natural number.


(1)2 = 1 (which is not greater than 1)


⇒ (1)2 >≠ 1


Hence, the given statement is false.



Question 59.

State whether the statements are true (T) or false (F).

The cube root of 8000 is 200.


Answer:

Given: cube root of 8000

As we know,


(200)3 = 8000000


⇒ 8000 ≠ cube root of 200


Hence, the given statement is false.



Question 60.

State whether the statements are true (T) or false (F).

There are five perfect cubes between 1 and 100.


Answer:

Given: perfect cubes between 1 and 100

i.e. 8, 27, 64, 125, 216, 343, 512 and 729.


we observe that there are 8 perfect cubes in between these.


Hence, the given statement is false.



Question 61.

State whether the statements are true (T) or false (F).

There are 200 natural numbers between 1002 and 1012.


Answer:

Given: natural numbers between 1002 and 1012

As we know, natural numbers between a and b = b-a-1


then natural numbers between 1002 and 1012 = 1012 – 1002 – 1


= (1012 – 1002)– 1


= (101 + 100)(101-100)-1


= (201)(1)-1


= 201 -1 = 200


Hence, the given statement is true.



Question 62.

State whether the statements are true (T) or false (F).

The sum of first n odd natural numbers is n2.


Answer:

Given: first n odd natural numbers

Odd natural number will be = 2n-1


As we know, sum of odd natural numbers =


= n2 + n-n


= n2


Hence, the given statement is true.



Question 63.

State whether the statements are true (T) or false (F).

1000 is a perfect square.


Answer:

Given: 1000

Factors of 1000 = 2 ×2 × 2 × 2 × 5 × 5 × 5


= 23× 53


As we see, 1000 is a perfect cube not a perfect square.


Hence, the given statement is false.



Question 64.

State whether the statements are true (T) or false (F).

A perfect square can have 8 as its units digit.


Answer:

Given: perfect square

As we see, A perfect square can never have 8 at its unit’s place.


Hence, the given statement is false.



Question 65.

State whether the statements are true (T) or false (F).

For every natural number m (2m-1, 2m2-2m,2m2-2m + 1) is a Pythagorean triplet.


Answer:

Given: natural number m (2m-1, 2m2-2m,2m2-2m + 1)

For Pythagorean triplet square of one should be equal to sum of square of other two.


But it is not true for the given values.


(2m-1)2≠ (2m2-2m)2 + (2m2-2m + 1)2


(2m2-2m)2≠(2m-1)2 + (2m2-2m + 1)2


(2m2-2m + 1)2≠(2m2-2m)2 + (2m-1)2


Hence, the given statement is false.



Question 66.

State whether the statements are true (T) or false (F).

All numbers of a Pythagorean triplet are odd.


Answer:

Given: Pythagorean triplet

For Pythagorean triplet square of one should be equal to sum of square of other two.


Pythagorean triplet as 52 = 42 + 32


Here, we see 4 is not an odd number.


Hence, the given statement is false.



Question 67.

State whether the statements are true (T) or false (F).

For an integer a, a3 is always greater than a2.


Answer:

Given: integer a

For an integer (-1)


(-1)2 = 1


And (-1)3 = -1


-1 < 1


Here we see (-1)3 not greater than (-1)2


Hence, the given statement is false.



Question 68.

State whether the statements are true (T) or false (F).

If x and y are integers such that x2>y2, then x3>y3.


Answer:

Given: integer x and y

For an integer x and y as (-1) and (-2) respectively.


x2>y2⇒ (-2)2 > (-1)2 = 4 > 1 (true)


and x3>y3⇒ (-2)3 > (-1)3 = -8 > -1 (not true)


as -8 < -1


Hence, the given statement is false.



Question 69.

State whether the statements are true (T) or false (F).

If x and y be natural numbers. If x divides y, then x3 divides y3.


Answer:

Given: x and y be natural numbers.

If x divides y ⇒ is a natural number.


is also a natural number.


is also a natural number.


⇒ x3 divides y3


Hence, the given statement is true.



Question 70.

State whether the statements are true (T) or false (F).

If a2 ends in 5, then a3 ends in 25.


Answer:

Given: a

Let us take an example:


(35)2 = 1225 (ends in 5)


And (35)3 = 42875 (doesn’t ends in 25)


Hence, the given statement is false.



Question 71.

State whether the statements are true (T) or false (F).

If a2 ends in 9, then a3 ends in 7.


Answer:

Given: a

Let us take an example:


(7)2 = 49 (ends in 9)


And (7)3 = 343 (doesn’t ends in 7)


Hence, the given statement is false.



Question 72.

State whether the statements are true (T) or false (F).

The square root of a perfect square of n digits will have digits, if n is odd.


Answer:

Given: square root of a perfect square of n digit.

If perfect square of 3 digits then the square root has 2 digits. i.e.


If perfect square of 5 digits then the square root has 3 digits. i.e.


Which is true.


Hence, the given statement is true.



Question 73.

State whether the statements are true (T) or false (F).

Square root of a number x is denoted by .


Answer:

Given: Square root of a number x.

It is denoted as


Hence, the given statement is true.



Question 74.

State whether the statements are true (T) or false (F).

A number having 7 at its ones place will have 3 at the units place of its square.


Answer:

Given: 7 at unit place.

(7)2 = 49


(17)2 = 289


(27)2 = 729


And so on.


49, 289, 729 don’t have 3 at the units place.


Hence, the given statement is false.



Question 75.

State whether the statements are true (T) or false (F).

A number having 7 at its ones place will have 3 at the ones place of its cube.


Answer:

Given: 7 at unit place.

(7)3 = 343


(17)3 = 4913


(27)3 = 19683


And so on.


343, 4913, 19683 all have 3 at the units place.


Hence, the given statement is true.



Question 76.

State whether the statements are true (T) or false (F).

The cube of a one-digit number cannot be a two digit number.


Answer:

Given: one-digit number

(3)3 = 27


Which is a two digit number.


Hence, the given statement is false.



Question 77.

State whether the statements are true (T) or false (F).

Cube of an even number is odd.


Answer:

Given: even number

Cube of an even number = (2)3 = 8


Which is not an odd number.


Hence, the given statement is false.



Question 78.

State whether the statements are true (T) or false (F).

Cube of an odd number is even.


Answer:

Given: odd number

Cube of an odd number = (3)3 = 27


Which is not an even number.


Hence, the given statement is false.



Question 79.

State whether the statements are true (T) or false (F).

Cube of an even number is even.


Answer:

Given: even number

Cube of an even number = (2)3 = 8


Which is an even number.


Hence, the given statement is true.



Question 80.

State whether the statements are true (T) or false (F).

Cube of an odd number is odd.


Answer:

Given: odd number

Cube of an odd number = (3)3 = 27


Which is an odd number.


Hence, the given statement is true.



Question 81.

State whether the statements are true (T) or false (F).

999 is a perfect cube.


Answer:

Given: 999

Factors of 999 = 3 ×3 × 3 × 37


= 33×37


As we see, 999 is not a perfect cube.


Hence, the given statement is false.



Question 82.

State whether the statements are true (T) or false (F).

363×81 is a perfect cube.


Answer:

Given: 363×81

Factors of 363×81 = 3 ×11 × 11 × 3 × 3 ×3 × 3


= 33 ×11 × 11 × 3 × 3


As we see, 363×81 is not a perfect cube.


Hence, the given statement is false.



Question 83.

State whether the statements are true (T) or false (F).

Cube roots of 8 are + 2 and -2.


Answer:

Given: Cube roots of 8

Cube roots of 8 = 2 only


Hence, the given statement is false.



Question 84.

State whether the statements are true (T) or false (F).



Answer:

Given:

..(1)


..(2)


From (1) and (2)



Hence, the given statement is false.



Question 85.

State whether the statements are true (T) or false (F).

There is no cube root of a negative integer.


Answer:

Given: Cube roots of a negative integer.

Cube roots of -8 = -2 only


Hence, the given statement is false.



Question 86.

State whether the statements are true (T) or false (F).

Square of a number is positive, so the cube of that number will also be positive.


Answer:

Given: a number

(-2)2 = 4


(-2)3 = -8


-8 which is not a positive.


Hence, the given statement is false.



Question 87.

Write the first five square numbers.


Answer:

to find: first five square numbers

first five square numbers are:


(1)2, (2)2, (3)2, (4)2 and (5)2 = 1, 4, 9, 16 and 25.



Question 88.

Write cubes of first three multiples of 3.


Answer:

to find: cube of first three multiple of 3.

cube of first three multiple of 3 are:


(3)3, (6)3 and (9)3 = 27, 216 and 729.



Question 89.

Show that 500 is not a perfect squae.


Answer:

Given: 500

Factors of 500 = 2 ×2 × 5 × 5 × 5


= 22 × 53


As we see, 500 is not a perfect square.


Hence proved.



Question 90.

Express 81 as the sum of first nine consecutive odd numbers.


Answer:

given: 81

As we know,


(81) = (9)2 = 1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 = sum of first nine consecutive odd numbers.



Question 91.

Using prime factorisation, find which of the following are perfect squares.

(a) 484 (b) 11250

(c) 841 (d) 729


Answer:

(a) Given: 484

Factors of 484 = 2 ×2 × 11 × 11


= 22 × 112


As we see, 484 is a perfect square.


(b) Given: 11250


Factors of 11250 = 2 × 3 × 3 × 5× 5 × 5 × 5


= 21 × 32× 52× 52


As we see, 2 has no pair.


So, 11250 is not a perfect square.


(c) Given: 841


Factors of 841 = 29 ×29


= 292


As we see, 841 is a perfect square.


(d) Given: 729


Factors of 729 = 3 × 3 × 3 × 3 × 3 × 3


= 32× 32× 32


So, 729 is a perfect square.



Question 92.

Using prime factorisation, find which of the following are perfect cubes.

(a) 128 (b) 343

(c) 729 (d) 1331


Answer:

(a) Given: 128

Factors of 128 = 2 ×2 × 2×2×2×2×2


= 23 × 23×2


As we see, 128 is not a perfect cube.


(b) Given: 343


Factors of 343 = 7 × 7 × 7


= 73


So, 343 is a perfect cube.


(c) Given: 729


Factors of 729 = 3 × 3 × 3 × 3 × 3 × 3


= 33× 33


So, 729 is a perfect cube.


(d) Given: 1331


Factors of 1331 = 11 × 11 × 11


= 113


So, 1331 is a perfect cube.



Question 93.

Using distributive law, find the squares of

(a) 101 (b) 72


Answer:

(a) Given: 101

As we know,


(101)2 is to find using distributive law:


(101)2 = 101 × 101


= 101 (100 + 1)


= 10100 + 101


= 10201


(b) Given: 72


As we know,


(72)2 is to find using distributive law:


(72)2 = 72 × 72


= 72 (70 + 2)


= 5040 + 144


= 5184



Question 94.

Can a right triangle with sides 6 cm, 10 cm and 8 cm be formed? Give reason.


Answer:

Given: sides of triangle 6cm, 10cm and 8cm

As we know,


For right angle triangle, square of one side must equal to sum of square of other two sides.


i.e.


(10)2 = (6)2 + (8)2


100 = 36 + 64


⇒ 100 = 100


Hence, 6cm, 10cm and 8cm are sides of triangle.



Question 95.

Write the Pythagorean triplet whose one of the numbers is 4.


Answer:

Given:

We know that for any natural number greater than 1, (2m, m2-1, m2 + 1) is a the Pythagorean triplet.


So if one number is 2m then other two number are m2-1 and m2 + 1.


i.e. 2m = 4 (given)


⇒ m = 2


Then m2-1 = 22-1 = 4-1 = 3


And m2 + 1 = 22 + 1 = 4 + 1 = 5


Hence, Pythagorean triplet is 3, 4 and 5



Question 96.

Using prime factorisation, find the square roots of

(a) 11025 (b) 4761


Answer:

(a) Given: 11025

Factors of 11025 = 3 × 3× 5× 5× 7× 7


Then square roots of 11025 = 3 × 5 × 7


= 105


(b) Given: 4761


Factors of 4761 = 3 × 3× 23× 23


Then square roots of 4761 = 3 × 23


= 69



Question 97.

Using prime factorisation, find the cube roots of

(a) 512 (b) 2197


Answer:

(a) Given: 512

Factors of 512 = 2 × 2× 2× 2× 2× 2× 2× 2× 2


Then cube roots of 512 = 2× 2× 2


= 8


(b) Given: 2197


Factors of 2197 = 13 × 13 × 13


Then cube roots of 2197 = 13



Question 98.

Is 176 a perfect square? If not, find the smallest number by which it should be multiplied to get a perfect square.


Answer:

Given: 176

Factors of 176 = 2 × 2 × 2 × 2 × 11


As we see, 11 do not have a pair.


Hence 176 should be multiply with 11 to get perfect square.


⇒ 176 × 11 = 2 × 2 × 2 × 2 × 11 × 11


⇒ 1936 = 22× 22× 112


⇒ 1936 = 442


Which is perfect square of 44.



Question 99.

Is 9720 a perfect cube? If not, find the smallest number by which it should be divided to get a perfect cube.


Answer:

Given: 9720

Factors of 9720 = 2 × 2 × 2 × 3 × 3 × 3 × 3 × 3 × 5


As we see, 3 and 5 do not have a pair to make a cube.


Hence 9720 should be divided with 3 × 3 × 5 to get perfect cube.


⇒ 9720 should divide with 45.


Now, after division we get 216 = 63


Now, 216 is a perfect cube.



Question 100.

Write two Pythagorean triplets each having one of the numbers as 5.


Answer:

Given:

We know that for any natural number greater than 1, (2m, m2-1, m2 + 1) is a the Pythagorean triplet.


So if one number is m2 + 1 then other two number are m2-1 and 2m.


i.e. m2 + 1 = 5 (given)


⇒ m2 = 4


⇒ m = 2


Then m2-1 = 22-1 = 4-1 = 3


And 2m = 2(2) = 4


Hence, Pythagorean triplet is 3, 4 and 5


Similarly another triplet is:


132 = 122 + 52


Hence, 3,4,5 and 5,12,13 are two Pythagorean triplet.



Question 101.

By what smallest number should 216 be divided so that the quotient is a perfect square. Also find the square root of the quotient.


Answer:

Given: 216

Factors of 216 = 2 × 2 × 2 × 3 × 3 × 3


As we see, 2 and 3 do not have pair.


Hence 216 should be divided with 2 × 3 to get perfect square.


⇒ 216 should divide with 6.


Now, after division we get 36 = 62


Now, 36 is a perfect square and 6 is its square root.



Question 102.

By what smallest number should 3600 be multiplied so that the quotient is a perfect cube. Also find the cube root of the quotient.


Answer:

Given: 3600

Factors of 3600 = 2 × 2 × 2 × 2 × 3 × 3 × 5 × 5


As we see, 2,3 and 5 do not have a pair to make a cube.


Hence 3600 should be multipled with 2 × 2 × 3 × 5 to get perfect cube.


⇒ 3600 should multiply with 60.


Now, 3600× 60 = 216000


Now, 216000 is a perfect cube and the cube root is 2 × 2 × 3 × 5 i.e. 60.



Question 103.

Find the square root of the following by long division method.

(a) 1369 (b) 5625


Answer:

(a) Given: 1369


Hence, = 37


(b) Given: 5625



Hence, = 75



Question 104.

Find the square root of the following by long division method.

(a) 27.04 (b) 1.44


Answer:

(a) Given: 27.04


Hence, = 5.2


(b) Given: 1.44



Hence, = 1.2



Question 105.

What is the least number that should be subtracted from 1385 to get a perfect square? Also find the square root of the perfect square.


Answer:

Given: 1385


Hence, the least number is 16, which should be subtracted from 1385 to get a perfect square and the required perfect square number will be = 1385 – 16 = 1369


Then, = 37



Question 106.

What is the least number that should be added to 6200 to make it a perfect square?


Answer:

Given: 6200


Hence, (78)2 = 6084 < 6200


Next perfect sqaure is (79)2 = 6241


Hence, the least number is (6241-6200 = 41), which should be added to 6200 to get a perfect square and the required perfect square number will be 6241


Then, = 41



Question 107.

Find the least number of four digits that is a perfect square.


Answer:

Given: least number of four digit.

i.e. 1000



Hence, the least number of four digits that is a perfect square = 1000 + 24 = 1024



Question 108.

Find the greatest number of three digits that is a perfect square.


Answer:

Given: least number of three digit.


Now, if we subtract 38 from 999 we will get a perfect square


Hence, the three-digit number is 999-38 = 961


And = 31



Question 109.

Find the least square number which is exactly divisible by 3, 4, 5, 6, and 8.


Answer:

Given:

the least square number which is exactly divisible by 3, 4, 5, 6, and 8 is equal to L.C.M. 0f 3,4,5,6 and 8.



Hence, their L.C.M. is 2× 2× 2× 3× 5 = 120


As we see, (2× 2)× 2× 3× 5


i.e. 2,3 and 5 is not able to make their pair.


Hence, to make it perfect square, it must be multiplied with 2× 3× 5 = 30


As, 120× 30 = 3600


Hence 3600 is least square number which is exactly divisible by 3, 4, 5, 6, and 8.



Question 110.

Find the length of the side of a square if the length of its diagonal is 10 cm.


Answer:

Given: length of diagonal = 10cm

i.e. let side of square (AB) = xcm



length of diagonal (AD)2 = (AB)2 + (BD)2


(10)2 = (x)2 + (x)2


⇒ 100 = 2x2


⇒ x2 = 50



Side of square =



Question 111.

A decimal number is multiplied by itself. If the product is 51.84. find the number.


Answer:

Given:

Let the number is y


Acc. To condition:


y × y = 51.84


⇒ y2 = 51.84





Hence, required number is 7.2



Question 112.

Find the decimal fraction which when multiplied by itself gives 84.64.


Answer:

Given:

Let the number is y


Acc. To condition:


y × y = 84.64


⇒ y2 = 84.64





Hence, required number is 9.2



Question 113.

A farmer wants to plough his square field of side 150m. How much area will he have to plough?


Answer:

Given: square field of side = 150m

Area of square = side × side


= 150 × 150


= 22500m2


The area farmer have to plough = 22500m2



Question 114.

What will be the number of unit squares on each side of a square graph paper if the total number of unit squares is 256?


Answer:

Given:

Let the number is y.


Then the number of unit square = y × y = y2


But total number of unit squares = 256


⇒ y2 = 256


Then y = = 16


Hence, the number of unit squares = 16



Question 115.

If one side of a cube is 15 m in length, find its volume.


Answer:

Given: cube of side = 15m

volume of cube = (side)3


= (15)3


= 3375m3


Hence, volume of cube = 3375m3



Question 116.

The dimensions of a rectangular field are 80 m and 18 m. Find the length of its diagonal.


Answer:

Given: dimensions of a rectangular field

i.e. let length (AB) = 80m


and breadth (BD) = 18m



length of diagonal (AD) =





Question 117.

Find the area of a square field if its perimeter is 96 m.


Answer:

Given: perimeter = 96 m

Let length of square = a


Then 4a = 96m


⇒ a = 24m


Area of square = side × side


= 24 × 24


= 576m2



Question 118.

Find the length of each side of a cube if its volume is 512 cm3.


Answer:

Given: cube of volume = 512cm3

volume of cube = (side)3


512 = (x)3


⇒ x3 = 8× 8× 8 = 83


Hence, side of cube (x) = 8cm



Question 119.

Three numbers are in the ratio 1 : 2 : 3 and the sum of their cubes is 4500. Find the numbers.


Answer:

Given:

Let the three numbers are 1x, 2x and 3x


Acc. To given condition:


i.e (1x)3 + (2x)3 + (3x)3 = 4500


⇒ (x)3 + 8(x)3 + 27 (x)3 = 4500


⇒36(x)3 = 4500


⇒ (x)3 = 125 = 53


⇒ x = 5


Hence, numbers are 1(5) = 5


2(5) = 10


3(5) = 15



Question 120.

How many square metres of carpet will be required for a square room of side 6.5 m to be carpeted.


Answer:

Given:

Let length of square = 6.5m


Area of square = side × side


= 6.5 × 6.5


= 42.25m2



Question 121.

Find the side of a square whose area is equal to the area of a rectangle with sides 6.4 m and 2.5 m.


Answer:

Given:

Length of rectangle (l) = 6.4m


Breadth of rectangle (b) = 2.5m


Area of rectangle = l× b


= 6.4 × 2.5


= 16m2


Then area of square = 16m2 (equal to rectangle)


As we know,


Area of square = side × side


16 = (side)2


42 = (side)2


⇒ side = 4m



Question 122.

Difference of two perfect cubes is 189. If the cube root of the smaller of the two numbers is 3, find the cube root of the larger number.


Answer:

Given: Difference of two perfect cubes = 189.

The cube root of the smaller of the two numbers = 3


The cube of the smaller of the two numbers = 33 = 27


Let the other number = x


Acc. To given condition:


i.e. x3 – 27 = 186


⇒ x3 = 186 + 27


⇒ x3 = 216


⇒ x3 = 63


⇒ x = 6


Then, the cube root of the greater of the two numbers = 6



Question 123.

Find the number of plants in each row if 1024 plants are arranged so that number of plants in a row is the same as the number of rows.


Answer:

Given:

Let the number of plants in each row = y


number of plants in a row = the number of rows = y


Hence, total plants = y × y


Acc. To given condition:


Y2 = 1024


⇒ y2 = 32 × 32


⇒ y2 = 322


⇒ y = 32


Hence, the number of plants in each row = 32



Question 124.

A hall has a capacity of 2704 seats. If the number of rows is equal to the number of seats in each row, then find the number of seats in each row.


Answer:

Given:

Let the number of seats in each row = y


number of seats in a row = the number of rows = y


Hence, total seats = y × y


Acc. To given condition:


Y2 = 2704


⇒ y2 = 52 × 52


⇒ y2 = 522


⇒ y = 52


Hence, the number of seats in each row = 52



Question 125.

A General wish to draw up his 7500 soldiers in the form of a square. After arranging, he found out that some of them are left out. How many soldiers were left out?


Answer:

Given: 7500 soldier

He is arranging in a form of sqaue. 7500 must complete the square.


If not then the remaining will be left out soldier.



Hence, the number of soldiers were left out = 104



Question 126.

8649 students were sitting in a lecture room in such a manner that there were as many students in the row as there were rows in the lecture room. How many students were there in each row of the lecture room?


Answer:

Given:

Let the number of students in each row = y


number of students in a row = the number of rows = y


Hence, total students = y × y


Acc. To given condition:


Y2 = 8649


⇒ y2 = 93 × 93


⇒ y2 = 932


⇒ y = 93


Hence, the number of students in each row = 93



Question 127.

Rahul walks 12 m north from his house and turns west to walk 35 m to reach his friend’s house. While returning, he walks diagonally from his friend’s house to reach back to his house. What distance did he walk while returning?


Answer:

Given:


AC = ?


(AC) =




Hence, diagonal distance = 37m



Question 128.

A 5.5 m long ladder is leaned against a wall. The ladder reaches the wall to a height of 4.4 m. Find the distance between the wall and the foot of the ladder.


Answer:

Given:


Let distance between the wall and the foot of the ladder = (AB) = xm


(BC)2 = (AC)2 + (AB)2


⇒ (5.5)2 = (4.4)2 + (x)2


⇒ (x)2 = (5.5)2 - (4.4)2


⇒ (x)2 = 30.35 – 19.36


⇒ (x)2 = 10.89 = (3.3)2


⇒ (x) = 3.3


Hence, distance between the wall and the foot of the ladder = (AB) = 3.3m



Question 129.

A king wanted to reward his advisor, a wise man of the kingdom. So he asked the wiseman to name his own reward. The wiseman thanked the king but said that he would ask only for some gold coins each day for a month. The coins were to be counted out in a pattern of one coin for the first day, 3 coins for the second day, 5 coins for the third day and so on for 30 days. Without making calculations. Find how many coins will the advisor get in that month?


Answer:

Given:

Acc. To given condition:


The total amount he will get at the end = 1 + 3 + 5 + …


As we see it an odd natural number series,


And the the number of terms (n) = 30


Sum of odd natural numbers = n2 = 302 = 900


He will get 900 coins in that month.



Question 130.

Find three numbers in the ratio 2 : 3 : 5, the sum of whose squares if 608.


Answer:

Given:

Let the three numbers are 2x, 3x and 5x


Acc. To given condition:


i.e (2x)2 + (3x)2 + (5x)2 = 608


⇒ 4(x)2 + 9(x)2 + 25 (x)2 = 608


⇒38(x)2 = 608


⇒ (x)2 = 16


⇒ x = 4


Hence, numbers are 2(4) = 8


3(4) = 12


5(4) = 20



Question 131.

Find the smallest square number divisible by each one of the numbers 8, 9 and 10.


Answer:

Given:

the least square number which is exactly divisible by 8, 9 and 10 is equal to L.C.M. 0f 8, 9 and 10.



Hence, their L.C.M. is 2× 2× 2× 3× 3× 5 = 360


As we see, (2× 2)× 2× (3× 3) × 5


i.e. 2 and 5 is not able to make their pair.


Hence, to make it perfect square, it must be multiplied with 2 × 5 = 10


As, 360× 10 = 3600


Hence 3600 is least square number which is exactly divisible by 8, 9 and 10.



Question 132.

The area of a square plot is m2. Find the length of one side of the plot.


Answer:

Given:

area of square plot = (equal to rectangle)


As we know,


Area of square = side × side








⇒ length of one side of the plot = m



Question 133.

Find the square root of 324 by the method of repeated substraction.


Answer:

Given: 324

Now, we subtract successive odd numbers starting from 1 as:


324 – 1 = 323


323 – 3 = 320


320 – 5 = 315


315 – 7 = 308


308 – 9 = 299


299 – 11 = 288


288 – 13 = 275


275 – 15 = 260


260 – 17 = 243


243 – 19 = 224


224 – 21 = 203


203 – 23 = 180


180 – 25 = 155


155 – 27 = 128


128 – 29 = 99


99 – 31 = 68


68 – 33 = 35


35 – 35 = 0


Here we see 324 reduces to 0 after subtracting 18 odd numbers.


So 324 is perfect square of 18.



Question 134.

Three numbers are in the ratio 2 : 3: 4. The sum of their cubes is 0.334125. Find the numbers.


Answer:

Given:

Let the three numbers are 2x, 3x and 4x


Acc. To given condition:


i.e (2x)3 + (3x)3 + (4x)3 = 0.334125


⇒ 8(x)3 + 27(x)3 + 64(x)3 = 0.334125


⇒99(x)3 = 0.334125


⇒ (x)3 = 0.003375





⇒ x = 0.015


Hence, numbers are 2(0.015) = 0.03


3(0.015) = 0.045


4(0.015) = 0.06



Question 135.

Evaluate :


Answer:

Given:



= 3 + 0.2 + 0.4


= 3.6



Question 136.

Solve:



Answer:

Given:




= {37}3


= 37 × 37 × 37


= 50653



Question 137.

Solve:



Answer:

Given:




= {44}3


= 44 × 44 × 44


= 85184



Question 138.

A perfect square number has four digits, none of which is zero. The digits from left to right have values that are : even, even, odd, even. Find the number.


Answer:

Given:

Let the perfect square is abcd.


Acc. To condition:


a = even number


b = even number


c = odd number


d = even number


then one of the number will be 2234.



Question 139.

Put three different numbers in the circles so that when you add the numbers at the end of each line you always get a

perfect square.



Answer:

Given:

Numbers in circles can be:


6 + 19 = 25 (perfect square)


19 + 30 = 49 (perfect square)


30 + 6 = 36 (perfect square)




Question 140.

The perimeters of two squares are 40 and 96 metres respectively. Find the perimeter of another square equal in area to the sum of the first two aquares.


Answer:

Given: perimeter of one square = 40 m

Let length of square = a1


Then 4a1 = 40m


⇒ a1 = 10m


Area of square = a1 × a1


= 10 × 10


= 100m2


perimeter of second square = 96 m


Let length of square = a2


Then 4a2 = 96m


⇒ a2 = 24m


Area of square = a2 × a2


= 24 × 24


= 576m2


Because, perimeter of another square equal in area to the sum of the first two squares.


Hence,


area of another square = 100 + 576 = 676m


Area of square = a3 × a3


676 = (a3)2


⇒ a3 = 26m


Hence, perimeter = 4a3


= 4 × 26 = 104m



Question 141.

A three-digit perfect square is such that if it is viewed upside down, the number seen is also a perfect square. What is the number?

[Hint: The digit 1, 0 and 8 stay the same when viewed upside down, whereas 9 becomes 6 and 6 becomes 9.]


Answer:

Given:

Three-digit perfect squares are 196 and 961, which looks same when seen upside down.



Question 142.

13 and 31 is a strange pair of numbers such that their squares 169 and 961 are also mirror images of each other. Can you find two other such pairs?


Answer:

Given:

(1) one such pair is 12 and 21


(12)2 = 144 and (21)2 = 441


(1) another such pair is 102 and 201


(102)2 = 10404 and (201)2 = 40401