The mean and standard deviation of 20 observations are found to be 10 and 2, respectively. On rechecking, it was found that an observation 8 was incorrect.
Calculate the correct mean and standard deviation in each of the following cases:
If wrong item is omitted
It is given in the question that,
Total number of observations (n) = 20
Also, incorrect mean = 20
And, incorrect standard deviation = 2
Thus, incorrect sum of observations = 200
Hence, correct sum of observations = 200 – 8
= 192
= 10.1
Thus, 
= 2080 – 64
= 2016
= 2.02
5