Question

Find the sum of the first 15 multiples of 8

• A. 1120
• B. 1040
• C. 960
• D. 880

Answer 1

Answer:

C. 960

$a_1=8,a_{15}=120,d=8$

$S_n=n/2(a_1+a_n)$

$=15/2(8+120)$

$=15/2\times128$

$=960$