The mean of 100 observations was calculated as 40. It was found later on that one of the observations was misread as 83 instead of 53. The correct mean is :

The mean of 100 observations = 40 It was found later on that one of the observations was misread as 83 instead of 53 , Difference = – 83 + 53 = – 30 ∴ Decrease in average = – 30 ÷ 100 = – 0.3 ∴ Required average = 40 – 0.3 = 39.7