Evaluate the series 12.1 + 13 +13.9 +...+ 32.8.

Answer 1

looks like an AS with a = 12.1 , d = .9

what is the term number of 32.8 ?
a + (n-1)d = termn
12.1 + (n-1)(.9) = 32.8
.9n- .9 = 20.7
.9n =21.6
n = 24

sum(24) = 12(first + last)
= 12(12.1 + 32.8) = 538.8

check my arithmetic