The mean of 40 items is 35. Later on, it was discovered that two items were misread as 36 and 29 instead of 63 and 22. Find the correct mean.

By formula,

Mean = $\dfrac{\text{Sum of observations}}{\text{No. of observations}}$

Given,

Mean of 40 items = 35

$\therefore 35 = \dfrac{\text{Sum of observations}}{40} \\[1em] \text{Sum of observations} = 40 \times 35 = 1400.$

Since,

Sum of two items were misread as 36 and 29 instead of 63 and 22.

Actual sum of observation = 1400 - 36 - 29 + 63 + 22

= 1420.

Correct mean = $\dfrac{1420}{40}$ = 35.5

Hence, the correct mean is 35.5