What is the average of first 40 natural numbers?

Correct option is D

Given: 
n = 40
sum of first n natural numbers is given by $$\frac{n(n+1)}{2}$$

​​Average of first 40 natural numbers = $$\frac{\text{sum of first 40 natural numbers}}{40}$$ = ​$$\frac{(40)(40+1)}{2\times40}=\frac{(40)(41)}{80}=20.5$$ (Ans.)​