Question

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

पर्याय

• 15

• 30

• 14

• 29

Answer 1

Given:
Mean of first n natural numbers = 15

\[\Rightarrow \frac{1 + 2 + 3 + . . . + n}{n} = 15\]

\[ \Rightarrow \frac{\frac{n\left( n + 1 \right)}{2}}{n} = 15\]

\[ \Rightarrow \frac{n + 1}{2} = 15\]

\[ \Rightarrow n + 1 = 30\]

\[ \Rightarrow n = 29\]