Find the sum of integers from 1 to 100 that are divisible by 2 or 5.

Answer

N/a

Explanation

Integers from 1 to 100, divisible by 2 :
2, 4, 6, 8, 10, 12, 14, 16, 18, 20, …, 100
and integers from 1 to 100, divisible by 5 :
5, 10, 15, 20, 25, 30, 35, 40, 45, 50, …, 100
Therefore, sum of integers form 1 to 100 which are divisible by 2 or 5
`= (2 + 4 + 6 + 8 + 10 + ... + 100) + (5 + 15 + 25 + ... + 95)`
(Leaving common terms from 2nd series)
`= 2(1 + 2 + 3 + 4 + 5 + ... + 50) + 5(1 + 3 + 5 + ... + 19)`
`= 2 * (50(50 + 1))/(2) + 5 * (10)/(2)[2.1 + (10 - 1)2]`
`= 50 xx 51 + 25[20] = 2550 + 500 = 3050`