Question

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

Answer 1

Sn= \frac{a1(1-r^n)}{1-r
}

a1=10
r=1/5
n=5

Sn= \frac{10(1-(1/5)^5)}{1-(1/5) }
Sn=12.496