Question

Find the sum of first 40 positive integers divisible by 6.

Answer 1

The positive integers that are divisible by 6 are

6, 12, 18, 24 …

It can be observed that these are making an A.P. whose first term is 6 and common difference is 6.

a = 6

d = 6

S₄₀ =?

= 20[12 + (39) (6)]

= 20(12 + 234)

= 20 × 246

= 4920