# The mean of 10 observations was calculated as 40. It was detected on rechecking that the value of 45 was wrongly copied as 15. Find the correct mean.

**Solution:**

Given, the mean of 10 observations was calculated as 40.

It was detected on rechecking that the value of 45 was wrongly copied as 15.

We have to find the correct __mean__.

We know, Mean = Sum of all observations/Number of observations

Number of observations = 10

Mean = 40

Now, 40 = sum of all observations/10

Sum of all observations = 10(40)

Incorrect sum = 400

Incorrect observation = 15

Correct observation = 45

Correct sum = Incorrect sum - incorrect observation + correct observation

= 400 - 15 + 45

= 400 + 30

= 430

Correct mean = correct sum / number of observation

= 430/10

= 43

Therefore, the correct mean is 43.

**✦ Try This: **The mean of 12 observations was calculated as 50. It was detected on rechecking that the value of 35 was wrongly copied as 65. Find the correct mean.

**☛ Also Check: **NCERT Solutions for Class 7 Maths Chapter 3

**NCERT Exemplar Class 7 Maths Chapter 3 Sample Problem 13**

## The mean of 10 observations was calculated as 40. It was detected on rechecking that the value of 45 was wrongly copied as 15. Find the correct mean.

**Summary:**

The mean of 10 observations was calculated as 40. It was detected on rechecking that the value of 45 was wrongly copied as 15. The correct mean is 43.

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