### The average of a collection of 20 measurements was calculated to tb 56 cm. But later it was found that a mistake had occurred in one of the measurement which was recorded as 64 cm., but should have been 61 cm. The correct average must be.

A. 53 cm B. 54.5 cm C. 55.85 cm D. 56.15 cm Answer: Option C

### Solution(By Apex Team)

$\begin{array}{l}\text{According to the question,}\\ \text{Correct average}\\ =\Large\frac{20 \times 56-64+61}{20} \\ =\Large\frac{1120-3}{20} \\ =\Large\frac{1117}{20} \\ =55.85 \mathrm{~cm} \end{array}$

A. 20
B. 21
C. 28
D. 32

A. 18
B. 20
C. 24
D. 30

A. 10 years
B. 10.5 years
C. 11 years
D. 12 years