Question

What is the sum of the first five terms of a geometric series with a1 = 20 and r = 1/4?

Answer 1

G.S : a/(1-r)
=20/(1-0.25)
=26.67

Answer 2

thats the limiting sum...

you need

\[S_{n} = \frac{a(1- r^n)}{1 - r}\]

a = 20, r = 0.25 and n = 5