### The average of the squares of first ten natural numbers is.

A. 35.5 B. 36 C. 37.5 D. 38.5 Answer: Option D

### Solution(By Apex Team)

As we know that average of square of “n” natural number is $\begin{array}{l}=\Large\frac{n(n+1)(2n+1)}{6n}\\ =\Large\frac{(n+1)(2n+1)}{6}\end{array}$ According to the question, Average of square of first ten natural number is $\begin{array}{l}=\Large\frac{(10+1)(20+1)}{6}\\ =\Large\frac{11\times21}{6}\\ =38.5\end{array}$

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