Statistics
Class 8th Mathematics (old) MHB Solution
- The marks obtained by 25 students in a science test are given below. (Marks out…
- Some peas were shelled and the number of peas in each post was recorded.…
- The ages (in years) of 40 children in a class are given below. Prepare a…
- The heights in centimetres of 30 children in a class are given below. Present…
- Observe the given frequency table and write the answers to the following…
- The blood groups of the persons who had donated blood at blood donation camp are…
- The frequency table of the ages of 40 students in a class is given below. Find…
- The record of daily rainfall (in centimetres) in Walwa village in the first 15…
- The money earned (in rupees) by each of the 40 scouts in the Khari Kamai project…
- The number of drivers finded for breaking traffic rules on each day in June at a…
Exercise 30
Question 1.The marks obtained by 25 students in a science test are given below. (Marks out of 30)
Using this data, answer the following question :
(1) What are the lowest marks obtained?
(2) How many students have obtained this lowest score?
(3) How many students have obtained 20 marks?
(4) What is the frequency of the score 27?
(5) How many students have scored more than 20 marks?
Answer:
(1) 7
(2) 2
(3) 3
(4) 2
(5) 7
Question 2.
Some peas were shelled and the number of peas in each post was recorded.
Prepare a frequency table of the above data.
Answer:
For making frequency table,
Lowest no of peas = 2
Highest no of peas = 6
Now, we will count frequency of each number from 2 to 6 and will write them in table form.
Question 3.
The ages (in years) of 40 children in a class are given below. Prepare a frequency table for this data
Answer:
Question 4.
The heights in centimetres of 30 children in a class are given below. Present the data in a frequency table.
Answer:
For making frequency table,
Shortest Height = 130 cm
Longest height = 140 cm
Now, we will count frequency of each height from 130 to 140 and will write them in table form.
Question 5.
Observe the given frequency table and write the answers to the following questions.
(1) About how many families does the table give data?
(2) How many families have 3 members?
(3) How many families have 5 members?
(4) How many families have the maximum number of members?
(5) How many families have less than 4 members?
Answer:
(1) No of families, N = Sum of all frequencies = 1 + 3 + 5 + 6 + 7 + 5 + 4 = 31
(2) No of families having 3 members = Frequency of family having 3 members = 5
(3) No of families having 5 members = Frequency of family having 5 members = 7
(4) No of families having maximum no of members = Frequency of family having 7 members = 4
(5) No of families having less than 4 members
= No of families having either 1 or 2 or 3 members = 1 + 3 + 5 = 7
Question 6.
The blood groups of the persons who had donated blood at blood donation camp are as follows.
Use this information to complete the table below.
(1) Which blood group has the smallest number of donors?
(2) Which blood group has the most donors?
(3) How many donors are of the ‘B’ blood group?
(4) What was the total number of donors at the camp?
Answer:
(1) As AB has a frequency of 4, that is minimum therefore AB has the smallest number of donors
(2) As A has a frequency of 10, that is maximum therefore A has most donors.
(3) frequency corresponding to 'B' blood group is 7, therefore 'B' has 7 donors.
(4) Total no of donors, N = Sum of all frequencies = 10 + 7 + 4 + 9 = 30
Exercise 31
Question 1.The frequency table of the ages of 40 students in a class is given below. Find their mean age.
Answer:
We know that,
Mean, 
Where, N is the sum of total frequencies
From above data,
Hence, mean is 11.875.
Question 2.
The record of daily rainfall (in centimetres) in Walwa village in the first 15 days of September is given below.
2.5, 1.5, 4.0, 3.0, 0.5, 5.0, 5.5, 4.0, 2.5, 3.5, 6.0, 0.5, 0.5, 4.5, 1.5.
Find the mean rainfall for these 15 days.
Answer:
Let's make a frequency table for above data
We know that,
Mean,
Where, N is the sum of total frequencies
From above data,
Hence, mean is 3.
Question 3.
The money earned (in rupees) by each of the 40 scouts in the Khari Kamai project is given below.
Make a frequency table for this data and find the mean.
Answer:
Let's make a frequency table for above data
We know that,
Mean,
Where, N is the sum of total frequencies
From above data,
Hence, mean is 7.65.
Question 4.
The number of drivers finded for breaking traffic rules on each day in June at a certain square is as follows –
From this data, make a frequency table and find the mean.
Answer:
Let's make a frequency table for above data
We know that,
Mean,
Where, N is the sum of total frequencies
From above data,
Hence, mean is 2.