Question

Sum of first 15 multiples of 8 is:

Options

• 960

• 660

• 1200

• 1060

Answer 1

960

Explanation:

8 + 16 + 24 ...........15^th term

a = 8     d = 8

n = 15    sn = ?

`"S"_15=15/2[2(8)+(15-1)8]`

`"S"_15=15/2[16+112]`

`"S"_15=15/2[128]=15xx64=960`