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.

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

Solution:

(c) 64.91

Mean of 100 items = 64

Sum of 100 items $=64 \times 100=6400$

Correct sum $=(6400+36+90-26-9)=6491$

Correct mean $=\frac{6491}{100}=64.91$