Question

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

Answer 1

Sum of the first n terms of a geometric sequence is Sn = a(1 - r^n)/(1 - r)
Sn = 20(1 - (1/4)^5)/(1 - 1/4) = 20(1 - 1/1024)/(3/4) = 20(1023/1024)/(3/4) = 26 41/64