Question

Find the sum of first 100 even natural numbers which are divisible by 5.

 

Answer 1

The first few even natural numbers which are divisible by 5 are 10, 20, 30, 40, ...

This is an AP in which a = 10, d = (20 – 10) = 10 and n = 100.

The sum of n terms of an AP is given by

`S_n = n/2 [2a + (n - 1)d]` 

= `(100/2) xx [2 xx 10 + (100 - 1) xx 10]`   ...[∵ a = 10, d = 10 and n = 100]

= 50 × [20 + 990] 

= 50 × 1010

= 50500

Hence, the sum of the first hundred even natural numbers which are divisible by 5 is 50500.