Question

What is the value of the fourth term in a geometric sequence for which a1=30 and r=1/2

Answer 1

a(4) = 15/4

Explanation:

The general formula for a geometric series with common ratio r and first term a(1) is

a(n) = a(1)*r^(n - 1)

and so, if a(1) = 30 and r = 1/2, we have

a(n) = 30*(1/2)^(n - 1)

and the fourth term is then:

a(4) = 30*(1/2)^(4 - 1) = 30/8 = 15/4