Question

The mean of 40 observations was 250. It was detected that the value of 150 was wrongly copied as 110. Find the correct mean ?

• A. 251
• B. 400
• C. 125
• D. the mean will be the same

Answer 1

The correct option is A

251

$\overline{x}=\frac{\sum x}{40}$ = 250

Hence $\sum x$ = 250 x 40 = 10,000

$\to$ Incorrect Value of $\sum x$ = 10,000

Correct value of $\sum x$ = Incorrect Value of $\sum x$ - Incorrect Observation + Correct Observation
= 10,000 - 110 + 150
= 10,040

Correct Mean = $\frac{\text{correct value of}\sum x}{n}$
=$\frac{10,040}{40}$
= 251