The mean of 40 observations was 160. It was detected that the value of 165 was wrongly copied as 125. Find the correct mean.

Mean (average) of 40 observations=160

Total sum (incorrect) of 40 observations= $40\times 160$ = 6400

Since, 165 was wrongly copied as 125

$\therefore$ Correct sum of 40 observations = 6400-125-165=6440

Correct mean=$\frac{6400}{40}=161$