Find the sum of first 15 multiples of 8.
First 15 multiples of 8 are 8, 16, 24, 32,…………..
This, clearly is an AP
where,
a = 8
And,
d = 16 – 8 = 8
We know that,
Sum of first n terms of an AP,
⇒ S15 = 15 × 64
⇒ S15 = 960
Hence, sum of first 15 multiples of 8 = 960