Question

if the mean of fitst n natural number is 15 then find n​

Answer 1

Answer

Correct option is

D

29

The first n natural numbers are 1,2,3,...,n

Given that mean of n natural numbers is 15

⟹

n

1+2+3+...+n

=15 ———(1)

We know that sum of first n natural numbers is

2

n(n+1)

⟹1+2+3+...+n=

2

n(n+1)

———(2)

Substituting (2) in (1) we get

⟹

2n

n(n+1)

=15

⟹n+1=30⟹n=30−1=29