### Find the average of cubes of first 49 positive integers.

A. 30625 B. 1225 C. 30125 D. 6235 Answer: Option A

### Solution(By Apex Team)

Sum of cubes of first n positive consecutive numbers is $\Large=\frac{(n(n+1))^{2}}{4}$ $\begin{array}{l}\text{ Average }\\ =\Large\frac{(n(n+1))^2}{4}\\ \Rightarrow n=49\\ \Rightarrow\Large\frac{49(50)^2}{4}\\ \Rightarrow30625\end{array}$

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