Question

Arithmetic mean of 9 observations was calculated as 45. In doing so, an observation was wrongly taken as 42 instead of 24. What would then be the correct mean ?

Answer 1

Mean of 9 observations = 45

So, Sum of 9 observations = 45 $\times$ 9 = 405

While computing mean, 42 was taken instead of 24.

So, Correct sum of 9 observations = 405 - 42 + 24 = 387

Therefore, Actual mean of 9 observations $=\frac{\sum x_i}{N}$

$=\frac{38}{79}$

$=43$