Chapter 7: Statistics Exercise – 7.2

Question: 1

The number of telephone calls received at an exchange per interval for 250 successive one- minute intervals are given in the following frequency table:

Compute the mean number of calls per interval.

Solution:

Let be assumed mean (A) = 3

Mean number of cells = 3 + 135/250
= 885/250
= 3.54

Question: 2

Five coins were simultaneously tossed 1000 times, and at each toss the number of heads was observed. The number of tosses during which 0, 1, 2, 3, 4 and 5 heads were obtained are shown in the table below. Find the mean number of heads per toss.

Solution:

Let the assumed mean (A) = 2

Mean number of per toss = 2 + 470/1000 
= 2 + 0.47 
= 2.47 

Question: 3

The following table gives the number of branches and number of plants in the garden of a school.

Calculate the average number of branches per plant.

Solution:

Let the assumed mean (A) = 4

Average number of branches per plant = 4 + (-77/200) 
= 4 -77/200 
= (800 -77)/200
= 3.615

Question: 4

The following table gives the number of children of 150 families in a village

Find the average number of children per family.

Solution:

Let the assumed mean (A) = 2

Average number of children for family = 2 + 52/150
= (300 +52)/150 
= 352/150 
= 2.35 (approx) 

Question: 5

The marks obtained out of 50, by 102 students in a physics test are given in the frequency table below:

Find the average number of marks.

Solution:

Question: 6

The number of students absent in a class was recorded every day for 120 days and the information is given in the following

Find the mean number of students absent per day.

Solution:

Let mean assumed mean (A) = 3

Mean number of students absent per day = 3 + 63/120
= (360 + 63)/120
= 423/120
= 3.53

Question: 7

In the first proof of reading of a book containing 300 pages the following distribution of misprints was obtained:

Find the average number of misprints per page.

Solution:

Let the assumed mean (A) = 2

Average number of misprints per day = 2 + (- 381/300)
= (600-381)/300
= 219/300
= 0.73

Question: 8

Find the mean from the following frequency distribution of marks at a test in statistics:

Find the average number of accidents per worker.

Solution:

Let the assumed mean (A) = 2

Average no of accidents per day workers ⟹ x + (-187/160)
= 133/160
= 0.83

Question: 9

The number of telephone calls received at an exchange per interval for 250 successive one- minute intervals are given in the following frequency table:

Solution:

Let the assumed mean (A) = 25

Mean = 25 + (-1170)/400

= 22.075