Question

What is the sum of the first five terms of a geometric series with a1=10 and r=1/5?

Answer 1

here is formula for sum of geometric series
\[S = \frac{a_1 (1- r^n)}{1-r}\]

Answer 2

substituting...
\[S = \frac{10(1-(1/5)^5}{1- (1/5)}\]

Answer 3

So my answer would be 12.5?