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Rational Numbers

Class 8th Mathematics West Bengal Board Solution
Lets Do 3.1
  1. | Let's solve the equations below:(i) 5x = 30(ii) 2x + {x-1}/{2} = 5 (iii)…
  2. 5x = 30 Let’s solve the equations below:
  3. 2x + {x-1}/{2} = 5 Let’s solve the equations below:
  4. {x}/{5} + frac {2}/{7} = frac {x}/{10} Let’s solve the equations below:…
  5. {x}/{4} + frac {1}/{2} = frac {1}/{2} Let’s solve the equations below:…
Lets Do 3.2
  1. We shall get 0 by adding [ ] with 2/9
  2. We shall get 0 by adding with {2}/{9}
  3. We shall get 0 by adding with - {9}/{8}
  4. We shall get 0 by adding [ ] with - {9}/{8}
  5. We shall get 0 by adding with - ( - {5}/{2} )
  6. We shall get 0 by adding [ ] with - ( - {5}/{2} )
  7. We shall get 1 by multiplying with {5}/{8}
  8. We shall get 1 by multiplying [ ] with 5/8
  9. We shall get 1 by multiplying [ ] with - {3}/{9}
  10. We shall get 1 by multiplying with - {3}/{9}
  11. Lets multiply using commutative law and associative law {7}/{9} x ( - frac…
  12. Lets multiply using commutative law and associative law {7}/{9} x ( - frac…
Lets Work Out 3
  1. Let’s solve the following equations and express the roots in form {p}/{q} (where…
  2. Let’s solve the following equations and express the roots in form {p}/{q} (where…
  3. Let’s verify if y= {5}/{4} then –(-y)=y
  4. Let’s verify if y= {5}/{4} then –(-y)=y
  5. If x = - {3}/{8} then find the value ofA. 2x + 5B. x + {3}/{8} C. 5 – (-x)D.…
  6. If x = - {3}/{8} then find the value ofA. 2x + 5B. x + {3}/{8} C. 5 – (-x)D.…
  7. let’s write the appropriate number in the following boxes:A. {9}/{11} + ? = 0B. ? +…
  8. let’s write the appropriate number in the following boxes:A. {9}/{11} + ? = 0B. ? +…
  9. lets write the product by multiplying ( {7}/{18} ) with the reciprocal of ( -…
  10. lets write the product by multiplying ( {7}/{18} ) with the reciprocal of ( -…
  11. Find the value of the following with the help commutative Law and Associative Law.(i)…
  12. Find the value of the following with the help commutative Law and Associative Law.(i)…
  13. Let’s put the rational numbers in the number line {1}/{4} , frac {3}/{4} , - frac…
  14. Let’s put the rational numbers in the number line {1}/{4} , frac {3}/{4} , - frac…
  15. Let’s write 4 rational number which are bigger than 1 but smaller than 2.…
  16. Let’s write 4 rational number which are bigger than 1 but smaller than 2.…
  17. Find rational numbers between {3}/{5} frac {1}/{2} [Hints: - {3}/{5} = - frac…
  18. Find rational numbers between {3}/{5} frac {1}/{2} [Hints: - {3}/{5} = - frac…
  19. {1}/{3} frac {3}/{5} write five rational numbers between the two rational numbers…
  20. {1}/{3} frac {3}/{5} write five rational numbers between the two rational numbers…
  21. {4}/{3} frac {3}/{7} [Hint: let’s make the denominator same {1}/{3} = frac…
  22. {4}/{3} frac {3}/{7} [Hint: let’s make the denominator same {1}/{3} = frac…
  23. {1}/{4} frac {1}/{2} write five rational numbers between the two rational numbers…
  24. {1}/{4} frac {1}/{2} write five rational numbers between the two rational numbers…

Lets Do 3.1
Question 1.

| Let's solve the equations below:

(i) 5x = 30

(ii)

(iii)

(iv)


Answer:

(i) 5x = 30


X =


X = 6


x = 6.


(ii) = 5


5x – 1 = 10


5x = 11


X =


X = 2.2


x = 2.2


(iii) = 0



7x +20 = 0


7x = -20


X = -


x = -


(iv) + - = 0



X = 0


x = 0



Question 2.

Let’s solve the equations below:

5x = 30


Answer:

This is an algebraic equation which is univariate as it contains only one variable, that is, x.

We have


5x = 30


We need to solve this equation.


That is, we need to find the value of variable x.


We will use any kind of mathematical operation (addition, subtraction, multiplication or division) in order to find x.


Note that, 5 is multiplied to x on L.H.S of the equation.


So, divide 5 on both sides of the equation so that we have x idle on L.H.S.



⇒ x = 6


Thus, we have solved the equation and x = 6.



Question 3.

Let’s solve the equations below:




Answer:

This is an algebraic equation which is univariate as it contains only one variable, that is, x.

We have



We need to solve this equation.


That is, we need to find the value of variable x.


We will use any kind of mathematical operation (addition, subtraction, multiplication or division) in order to find x.


Here, we can simplify the equation by taking L.C.M of the denominators on L.H.S of the equation.


Denominator of 2x = 1


Denominator of = 2


L.C.M (1, 2) = 2


Therefore, multiplying 2 by 2x and 1 by (x – 1), we get



Now start simplifying it as much as possible. For instance, multiply 2 on both sides,



⇒ (2 × 2x) + (1 × (x – 1)) = 10


⇒ 4x + (x – 1) = 10


⇒ 4x + x – 1 = 10


Constants of the variable can be operated, so


⇒ (4x + x) – 1 = 10


⇒ 5x – 1 = 10


Take the constant 1 on R.H.S. The negative sign on L.H.S will become positive on R.H.S.


⇒ 5x = 10 + 1


⇒ 5x = 11


Divide 5 on both sides to leave x idle.




Thus, we have solved the equation and .



Question 4.

Let’s solve the equations below:




Answer:

This is an algebraic equation which is univariate as it contains only one variable, that is, x.

We have



We need to solve this equation.


That is, we need to find the value of variable x.


We will use any kind of mathematical operation (addition, subtraction, multiplication or division) in order to find x.


Here, we can simplify the equation by taking L.C.M of the denominators on L.H.S of the equation.


Denominator of = 5


Denominator of = 7


L.C.M (5, 7) = 35


Therefore, multiplying 7 by x and 5 by 2, we get



Now, simplify it as much as possible. Cross multiplying, 35 by x and 10 by (7 × x) + (5 × 2), we get


⇒ 10 × ((7 × x) + (5 × 2)) = 35 × x


⇒ 10 × (7x + 10) = 35x


By distributive law, multiply 10 by 7x and by 10.


⇒ (10 × 7x) + (10 × 10) = 35x


⇒ 70x + 100 = 35x


Take x’s on one side and constants on the other. Here, shift 35x on L.H.S (positive sign of 35 will become negative) and 100 on R.H.S (positive sign of 100 will become negative).


⇒ 70x – 35x = -100


⇒ 35x = -100


Divide 35 on both sides to leave x idle.




Thus, we have solved the equation and .



Question 5.

Let’s solve the equations below:




Answer:

This is an algebraic equation which is univariate as it contains only one variable, that is, x.

We have



We need to solve this equation.


That is, we need to find the value of variable x.


We will use any kind of mathematical operation (addition, subtraction, multiplication or division) in order to find x.


Here,


Shift the constant � from L.H.S to R.H.S, it’s positive sign will become negative.




Multiply by 4 on both sides so that x can be left idle.



⇒ x = 0


Thus, we have solved the equation and x = 0.




Lets Do 3.2
Question 1.

We shall get 0 by adding [ ] with 2/9


Answer:

According to the question,


Let’s assume the number (to be calculated) to be ‘x’.


So,


X + = 0


X = -


x = -



Question 2.

We shall get 0 by adding with


Answer:

Let x be the number to which when 2/9 is added, we shall get 0.


We need to find x.


So, formulate it into a mathematical equation using operators and numbers.


x is added to 2/9 can be written as,



Now, when x is added to 2/9, we get 0. That is,



To solve for x, shift 2/9 from L.H.S to R.H.S, positive sign of 2/9 will become negative.




Thus, we shall get 0 by adding with .



Question 3.

We shall get 0 by adding with


Answer:

Let x be the number to which when -9/8 is added, we shall get 0.


We need to find x.


So, formulate it into a mathematical equation using operators and numbers.


x is added to -9/8 can be written as,



Or,



Now, when x is added to -9/8, we get 0. That is,



To solve for x, we need to shift 9/8 to R.H.S. Negative sign of 9/8 will become positive.




Thus, we shall get 0 by adding with .



Question 4.

We shall get 0 by adding [ ] with


Answer:

According to the question,


Let’s assume the number (to be calculated) to be ‘x’.


So,


X +( - ) = 0


X =


x =



Question 5.

We shall get 0 by adding with


Answer:

Let x be the number to which when is added, we shall get 0.


We need to find x.


So, formulate it into a mathematical equation using operators and numbers.


x is added to can be written as,



Or,



Or,



Now, when x is added to , we get 0. That is,



To solve for x, we need to shift 5/2 to R.H.S. Positive sign of 9/8 will become negative.




Thus, we shall get 0 by adding with .



Question 6.

We shall get 0 by adding [ ] with


Answer:

According to the question,


Let’s assume the number (to be calculated) to be ‘x’.


So,


X +( - ) = 0


X =


x =



Question 7.

We shall get 1 by multiplying with


Answer:

Let x be the number to which when is multiplied, we shall get 1.


We need to find x.


So, formulate it into a mathematical equation using operators and numbers.


x is multiplied with can be written as,



Or,



Now, when x is multiplied with , we get 1. That is,



To solve for x, multiply 8 on both sides.



⇒ 5x = 8


Dividing 5 on both sides to leave x idle, we get




Thus, we shall get 1 by multiplying with .



Question 8.

We shall get 1 by multiplying [ ] with 5/8


Answer:

According to the question,


Let’s assume the number (to be calculated) to be ‘x’.


So,


x = 1


X =


x =



Question 9.

We shall get 1 by multiplying [ ] with


Answer:

According to the question,


Let’s assume the number (to be calculated) to be ‘x’.


So,


x(-) = 1


X = -


x = - 3



Question 10.

We shall get 1 by multiplying with


Answer:

Let x be the number to which when is multiplied, we shall get 1.


We need to find x.


So, formulate it into a mathematical equation using operators and numbers.


x is multiplied with can be written as,



Or,



Or,



Now, when x is multiplied with , we get 1. That is,



To solve for x, multiply -3 on both sides.



⇒ x = -3


Thus, we shall get 1 by multiplying -3 with .



Question 11.

Lets multiply using commutative law and associative law




Answer:

As per the Commutative Law of multiplication,


a b = b a = ab = ba


The product is , which will result in calculating either of the following expressions :-




As per the Associative Law of multiplication,


a (b c d) = (ab c) d = abcd = abcd


The product is , which will result in calculating either of the following expressions :-



•[{


Hence proved, both the laws (Associative & Commutative) of multiplication.



Question 12.

Lets multiply using commutative law and associative law




Answer:

We must understand that,

Commutative law, in mathematics, either of two laws relating to number operations of addition and multiplication, stated symbolically: a + b = b + a and ab = ba.


Associative law, in mathematics, either of two laws relating to number operations of addition and multiplication, stated symbolically: (a + b) + c = a + (b + c), and a(bc) = (ab)c.


We have,



We can write as,



According to the commutative law of multiplication,



So,






Also, by associative law of multiplication,



We can solve it by any way.


So,





Thus, the answer is .




Lets Work Out 3
Question 1.

Let’s solve the following equations and express the roots in form (where q 0 and p, q are two integers)

A. 7x=14

B. 4p+32=0

C. 11x=0

D. 5m-3=0

E. 9y + 18 =0

F. t=8-12

G. 6y = 5 + y

H. 2x +___ = ____ ( put the rational number myself)


Answer:

A. 7x=14



⇒ x = 2


It can be written in rational form i.e. form as:



B. 4p = -32



It can be written in rational form i.e. form as:



C. 11x = 0


x = 0


It can be written in rational form i.e. form as:



D. 5m=3


It can be written in rational form i.e. form as:



E. 9y + 18 =0


9y = -18



Y = -2


It can also be written in a rational form as


F. t = 8 - 12


t=-4


It can be written in rational form i.e. form as:



G. 6y-y=5


⇒ 5y=5



It can be written in rational form i.e. form as:



H. 2x + = ______


Let ? = 1/2


So 2x + 1/2 = 1/2


2x = 1/2 - 1/2


2x = 0


x = 0


It can be written in rational form i.e. form as:




Question 2.

Let’s solve the following equations and express the roots in form (where q 0 and p, q are two integers)

A. 7x=14

B. 4p+32=0

C. 11x=0

D. 5m-3=0

E. 9y + 18 =0

F. t=8-12

G. 6y = 5 + y

H. 2x +___ = ____ ( put the rational number myself)


Answer:

A. 7x=14



⇒ x = 2


It can be written in rational form i.e. form as:



B. 4p = -32



It can be written in rational form i.e. form as:



C. 11x = 0


x = 0


It can be written in rational form i.e. form as:



D. 5m=3


It can be written in rational form i.e. form as:



E. 9y + 18 =0


9y = -18



Y = -2


It can also be written in a rational form as


F. t = 8 - 12


t=-4


It can be written in rational form i.e. form as:



G. 6y-y=5


⇒ 5y=5



It can be written in rational form i.e. form as:



H. 2x + = ______


Let ? = 1/2


So 2x + 1/2 = 1/2


2x = 1/2 - 1/2


2x = 0


x = 0


It can be written in rational form i.e. form as:




Question 3.

Let’s verify if y=then –(-y)=y


Answer:

Consider –(-y)




= y


= RHS


Hence –(-y)=y



Question 4.

Let’s verify if y=then –(-y)=y


Answer:

Consider –(-y)




= y


= RHS


Hence –(-y)=y



Question 5.

If x = - then find the value of

A. 2x + 5

B. x +

C. 5 – (-x)

D. ? = -(-x)


Answer:

A. Put in 2x + 5.



The L.C.M of 1 and 4 is 4.




B. Put



C. Put





D. Let x = 5


Now –(-5) = 5


Hence x = -(-x)



Question 6.

If x = - then find the value of

A. 2x + 5

B. x +

C. 5 – (-x)

D. ? = -(-x)


Answer:

A. Put in 2x + 5.



The L.C.M of 1 and 4 is 4.




B. Put



C. Put





D. Let x = 5


Now –(-5) = 5


Hence x = -(-x)



Question 7.

let’s write the appropriate number in the following boxes:

A. ? = 0

B. ? + =0

C. × ? = 1

D. -5 × ? = 1

E. × ? = 1

F. =


Answer:

A. Let the number in the box be x.




B. Let the number be x.




C. Let the number be x.




D. Let the number be x.




E. Let the number be x.




F. Let the number be x.






Question 8.

let’s write the appropriate number in the following boxes:

A. ? = 0

B. ? + =0

C. × ? = 1

D. -5 × ? = 1

E. × ? = 1

F. =


Answer:

A. Let the number in the box be x.




B. Let the number be x.




C. Let the number be x.




D. Let the number be x.




E. Let the number be x.




F. Let the number be x.






Question 9.

lets write the product by multiplying with the reciprocal of


Answer:

Reciprocal of


∴ the product will be-





Question 10.

lets write the product by multiplying with the reciprocal of


Answer:

Reciprocal of


∴ the product will be-





Question 11.

Find the value of the following with the help commutative Law and Associative Law.

(i)

(ii)


Answer:

(i) (Using Commutative law)


(Using Associative law)







(ii) (Using Commutative law)







Question 12.

Find the value of the following with the help commutative Law and Associative Law.

(i)

(ii)


Answer:

(i) (Using Commutative law)


(Using Associative law)







(ii) (Using Commutative law)







Question 13.

Let’s put the rational numbers in the number line


Answer:



Question 14.

Let’s put the rational numbers in the number line


Answer:



Question 15.

Let’s write 4 rational number which are bigger than 1 but smaller than 2.


Answer:

We know,


Now, multiplying and dividing both by 5, we get-



Therefore, the four in-between rational numbers can be-




Question 16.

Let’s write 4 rational number which are bigger than 1 but smaller than 2.


Answer:

We know,


Now, multiplying and dividing both by 5, we get-



Therefore, the four in-between rational numbers can be-




Question 17.

Find rational numbers between

[Hints: ]


Answer:

To find the in between rational numbers we’ll first make the denominator same.

So, here (multiplying and dividing by 2)


Similarly, (multiplying and dividing by 5)


Now, we can easily find the between rational numbers by taking the minimum and maximum values of numerator from given values. Here minimum value is -6 and maximum is 5.


∴ the rational numbers, which lies in between are-




Question 18.

Find rational numbers between

[Hints: ]


Answer:

To find the in between rational numbers we’ll first make the denominator same.

So, here (multiplying and dividing by 2)


Similarly, (multiplying and dividing by 5)


Now, we can easily find the between rational numbers by taking the minimum and maximum values of numerator from given values. Here minimum value is -6 and maximum is 5.


∴ the rational numbers, which lies in between are-




Question 19.

write five rational numbers between the two rational numbers given below.




Answer:

To find the in between numbers, we’ll first make the denominator same which will be the LCM of denominator of both the values.


Now, LCM(3,5)=15


∴ on multiplying and dividing by 5, we get-



And similarly,


On multiplying and dividing by 3, we get-



Now, the rational numbers in between will be-



But here we are getting 3 numbers only


To get more number we can now make the denominator different, likewise if we again multiply and divide the no. by 2, we get-



Therefore, the five numbers can be-




Question 20.

write five rational numbers between the two rational numbers given below.




Answer:

To find the in between numbers, we’ll first make the denominator same which will be the LCM of denominator of both the values.


Now, LCM(3,5)=15


∴ on multiplying and dividing by 5, we get-



And similarly,


On multiplying and dividing by 3, we get-



Now, the rational numbers in between will be-



But here we are getting 3 numbers only


To get more number we can now make the denominator different, likewise if we again multiply and divide the no. by 2, we get-



Therefore, the five numbers can be-




Question 21.

write five rational numbers between the two rational numbers given below.



[Hint: let’s make the denominator same ]


Answer:

To find the in between numbers, we’ll first make the denominator same which will be the LCM of denominator of both the values.

Now, LCM(3,7)=21


∴ on multiplying and dividing by 7, we get-



And similarly,


On multiplying and dividing by 3, we get-



Now, the five rational numbers in between can be-




Question 22.

write five rational numbers between the two rational numbers given below.



[Hint: let’s make the denominator same ]


Answer:

To find the in between numbers, we’ll first make the denominator same which will be the LCM of denominator of both the values.

Now, LCM(3,7)=21


∴ on multiplying and dividing by 7, we get-



And similarly,


On multiplying and dividing by 3, we get-



Now, the five rational numbers in between can be-




Question 23.

write five rational numbers between the two rational numbers given below.




Answer:

To find the in between numbers, we’ll first make the denominator same which will be the LCM of denominator of both the values.

Now, LCM(4,2)= 4


∴ on multiplying and dividing by 1, we get-



And similarly,


On multiplying and dividing by 2, we get-



To get more number we can now make the denominator different from LCM, likewise if we again multiply and divide the no. by 6, we get-



Therefore, the five numbers can be-




Question 24.

write five rational numbers between the two rational numbers given below.




Answer:

To find the in between numbers, we’ll first make the denominator same which will be the LCM of denominator of both the values.

Now, LCM(4,2)= 4


∴ on multiplying and dividing by 1, we get-



And similarly,


On multiplying and dividing by 2, we get-



To get more number we can now make the denominator different from LCM, likewise if we again multiply and divide the no. by 6, we get-



Therefore, the five numbers can be-