Question

The calculated mean of 50 observations was 80. It was later discovered observation 19 was recorded by mistake as 91. What was the correct mean?

Answer 1

The no . of observations $50$

The mean of Observations $80$

The sum of observations $50\times 80=4000$

So wrong observation is $91$

The correct one is $19$

The sum of observations is $4000-91+19=3928$

The correct mean is $\frac{3928}{50}=78.56$