Question

Find the sum of first 15 multiples of 8​

Answer 1

Answer:
960.
Explanation:
That is 8 + 2(8) + 3(8) + ........ + 15*8
This is an arithmetic series with first term 8 and common difference 8.
Number of terms = 15.
Sum of n terms
= (n/2)[2a1 + d(n-1)]
So, sum of 15 terms
= (15/2)[2*8 + 8(15-1)]
= 7.5 * 120
= 960.