Question

If the sum of first n natural numbers is one fifth of the sum of their squares

Answer 1

Answer:

Step-by-step explanation:

Sum First n natural numbers is n(n+1)/2.

Sum of squares of First n natural numbers is n(n+1)(2n+1)/6.

n(n+1)/2={1/5[n(n+1)(2n+1)/6]}

1/2=1/5[(2n+1)/6]

2n+1=15.

2n=14.

n=7.