Question

Mean of 36 observations is 12. One observation 47 was misread as 74. Find the correct mean.

Answer 1

∑x/36 =12
∑x = 36 × 12 = 432

∴ incorrect value = 432

correct value = incorrect value ∑x - incorrect value + correct value
                     = 432 - 47 + 74
                       = 459

so the correct mean = ∑x / n = 459/36=12.75

Answer 2

mean=sum of all observations ÷no.of.observations
12=sum of all observations ÷36
12×36=sumof all observations
432=incorrect mean
432+(74-47)=459=correct sum of all numbers 459/36=correct mean 12.75=correct mean