Question

In a class test, the mean marks scored by a class of 40 students was calculated as 18.2. Later on, it was detected that the marks of one student was wrongly copied as 21 instead of 29. Find the correct mean.

Answer 1

Given:

Number of students = 40

Incorrect mean = 18.2

One student’s mark was recorded 21 instead of 29

Step-wise calculation:

1. Incorrect total

= 18.2 × 40 

= 728

2. Correct total

= 728 – 21 + 29 

= 736

3. Correct mean

= 736 ÷ 40 

= 18.4

The correct mean is 18.4.