Question

Determine which of the following is the sum of the first forty terms of GP if first term is 40 and the common ratio is -1/2.

1. 30.667

2. 26.667

3. None of the answers

4. -27

Answer 1

Step-by-step explanation:

a = 40

r = -1/2

n = 40

Sum of 40 terms of GP

$S = \frac{a(r^{n}-1) }{1-r} \\S = \frac{40[1-(-1/2)^{40} ]}{3/2}\\\\S = \frac{40(1)}{3/2}\\S = 26.667$