Question

Calculate S30 for the arithmetic sequence defined by {an}={3.1n-2}

a.) 91
b.) 113
c.) 1,381.5
d.) 1,397.5

Answer 1

c) 1,381.5.

Explanation:

First term = 3.1 *1 - 2 = 1.1

2nd term = 3.1*2 - 2 = 4.2

3rd term = 3.1*3 - 2 = 7.3

so the common difference d = 3.1.

S30 = (30/2) [ 2* 1.1 + (30-1) * 3.1)]

= 1,381.5.