Question

The mean of 100 items was found to be 64. Later on it was discovered that two items were misread as 26 and 9 instead of 36 and 90 respectively. The correct mean is
(a) 64.86
(b) 65.31
(c) 64.91
(d) 64.61

Answer 1

(c) 64.91

Mean of 100 items = 64
Sum of 100 items = $64\times 100=6400$
Correct sum = (6400 + 36 + 90 $-$ 26 $-$ 9) = 6491
$\mathrm{Correct}\mathrm{mean}=\frac{6491}{100}=64.91$