Question

The sum of all natural numbers from 100 to 300 which are exactly divisible by 4 or 5

Answer 1

Divisible by 5

AP is 100, 105...300

a1 = 100, an = 300 and d = 5

using

an = a + (n-1) d

(SOLVING IT)

n = 39

then using sn = n/2 [2a + (n-1) d]

(SOLVING IT)

sn = 30420

Divisible by 4

AP is 100, 104...300

a = 100, an = 300 and d = 4

using same formulas in respected steps

n = 51 and sn = 30600