Question

A class teacher has the following absentee record of 40 students of a class for the whole term. Find the mean number of days a student was absent
Number of days:
0−6
6−10
10−14
14−20
20−28
28−38
38−40
Number of students:
11
10
7
4
4
3
1

Answer 1

ASSUMED MEAN METHOD :  

In this method, first of all, one among xi 's is chosen as the assumed mean denoted  by ‘A’. After that the difference ‘di’ between ‘A’ and each of the xi's i.e di = xi - A is calculated .  

MEAN =  A +  Σfidi / Σfi

[‘Σ’ Sigma means ‘summation’ ]

★★ We may take Assumed mean 'A’ to be that xi which lies in the middle of x1 ,x2 …..xn.

FREQUENCY DISTRIBUTION TABLE IS IN THE ATTACHMENT  

From the table : Σfidi = - 181 ,  Σfi = 40

Let the assumed mean, A = 17

MEAN =  A +  Σfidi / Σfi

MEAN = 17 + (- 181/40)

= 17 - 181/40

= 17 - 4.525

= 12.475

Hence, the mean number of days a student was absent is 12.475.

HOPE THIS ANSWER WILL HELP YOU…

Answer 2

Answer:

Step-by-step explanation:

MEAN =  A +  Σfidi / Σfi

MEAN = 17 + (- 181/40)

= 17 - 181/40

= 17 - 4.525

= 12.475