Question

Find the sum of first 100 even number 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 – l0) = 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 xx10 +(100-1) xx 10 ]         [ ∵ a = 10 , d = 10 and n = 100]`

`= 50 xx[ 20+ 990]=50xx 1010 = 50500`

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