Question

If the mean of the first n natural numbers is 15, then n = (a) 15 (b) 30 (c) 14 (d) 29

Answer 1

The sum of the first n natural numbers is n(n + 1)/2, so the mean of the first n natural numbers is n(n + 1)/(2n) = (n + 1)/2.

(n + 1)/2 = 15

n + 1 = 30

n = 29

The correct answer is D.