Question

Find the sum of the first 10 multiples of 6.

Answer 1

First 10 multiples of 6 are 6, 12, 18, 24, 30, 36, 42, 48, 54, 60. 

This forms an AP with first term a = 6 and common difference, d = 6. 

`"S"_"n" = "n"/2[2"a" +("n"-1)"d"]`

⇒ `"S"_10 = 10/2 [2xx6+(10-1)6]`

⇒ S₁₀ = 5[12+54]

⇒ S₁₀ = 5 × 66 =330

Thus, sum of first 10 multiples of 6 is 330.