Question

The mean of 20 observations is 12.5 , by an error one observation is registered as -15 instead of 15.Find the correct mean.

Answer 1

mean of 20 observations =12.5
sum of 20 observations=12.5×20
                                     =250

wrong observation is -15
correct observation is 15
sum of 20 observations correctly=250+30
                                                   =280
mean=280/20
         =14