Question

The sum of the arithmetic series 5 + 11 + 17 +.+ 95 is

Answer 1

a = 5 d = 11-5 = 6
an or last term = 95
a+(n-1)d = 95
5+(n-1)6 = 95
5+6n-6 = 95
6n-1 = 95
6n = 96
n = 16
sn = n/2(a+ last term)
s16 = 16/2(5+95)
s16 = 8×100 = 800