Question

Mean of a data consisting 25 observations is 40,if one of the observation as53 instead of 28 then the correct mean is

Answer 1

[Hope the question meant: If one of the observation was wrongly entered as 28 instead of 53 or it was changed to 53 from 28]
Mean of 25 observations = 40
Sum Total of 25 observations = 25*40 = 1000
One of the observation was wrongly entered as 28 instead of 53.
The corrected sum total = 1000 - 28 + 53 = 1025
Correct mean = 1025/25 = 41

OR
One of the observation was changed to 53 from 28. Change in reading = 25. Corrected mean = Actual mean + (change in reading)/no: of observations     
= 40 + (53-28)/25 = 40 + 1 = 41.