Question

what is the sum of the first 5 terms if of a geometric series with a1=20 and r=1/4 the answer has to be an improper fraction

Answer 1

the sum of the term in a geometric sequence
Sn=$\frac{a1(1-r^n)}{1-r}$
where
there are n terms
r is common ratio
a1 is first term

Sn=$\frac{20(1-(1/4)^5)}{1-(1/4)}$
Sn=$\frac{20(1-(1/1024))}{3/4}$
Sn=$\frac{20(1023/1024)}{3/4}$
Sn=$\frac{1705}{64}$