Question

Evaluate each arithmetic series described.

a1= 10 d= 8 n= 11


A) 1116
B) 1120
C) 550
D) 1118

Answer 1

$S_n=\frac{a_1+a_n}{2}\cdot n\\\\a_1=10, \ d=8, \ n=11\\\\a_{11}=a_1+10d=10+10\cdot8=10+80=90\\\\S_{11}=\frac{10+90}{2}\cdot11=\frac{100}{2}\cdot11=50\cdot11=\boxed{550}\\\\\text{Answer}:\text{C})$