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

Answer: Option B

Difference = 53 - 83 = - 30
Change in average
= $$\frac{-30}{100}$$
= - 0.3
So, correct average
= 40 - 0.3
= 39.7