The sum of the first n terms in the infinite geometric sequence 1/4, 1/8, 1/16, ... is 15/32. Find n.
a1 = 1/4
r = 1/2
Sn = a1(1-r^n) / ( 1-r)
15/32 = 1/4(1- 1/2^n) /(1/2)
15/16 = 1-1/2 ^n
1/16 = 1/2 ^n
n= 4
+37159 
