Question

If the mean of first n natural number is 15, then n =

(a) 15
(b) 30
(c) 14
(d) 29

Answer 1

Given:

Mean of first n natural numbers = 15

$$\begin{gathered} \Rightarrow \frac{1+2+3+...+n}{n}=15 \\ \Rightarrow \frac{{\displaystyle \frac{n\left(n+1\right)}{2}}}{n}=15 \\ \Rightarrow \frac{n+1}{2}=15 \\ \Rightarrow n+1=30 \\ \Rightarrow n=29 \end{gathered}$$

Hence, the correct option is (d).