Find S10 for (-1) + (-7) + (-13) + (-19) +...

Question

A. 250
B. -280
C. (-23)
D. 132

C.

Answer 1

a = -1
d = -6
n = 10
sum(10) = (10/2)(-2 + 9(-6))
= 5(-56) = -280

looks like B)