Geometric series

A geometric series has first term a and common ratio r. Choose values for a, r and the number of terms, n, and look at the series displayed.
You will also be given the sum of the first n terms, Sn,and the value of a over 1-r.
What values of r make Sn and the value of a over 1-r similar?

Enter a value for a :    Enter a value for r :    Enter a value for n :

Sn =    a over 1-r =