What is the sum of first 17 terms of an AP, if the 1st term is -20 and last term is 28?

A 68

B 78

C 58

D 167

Correct Answer: Option A

First term of AP = a = -20 and last term = l = 28
Number of terms = n = 17
Sum of AP = n/2(a+l)=(17/2)(−20+28)=17×4=68