Asked by Anonymous

Given that the fourth term is 64 and the sum to infinity is 625, what is the value of u1 and the value of r?
Answered by oobleck
u1 * r^3 = 64
u1/(1-r) = 625
so, dividing,
r^3(1-r) = 64/625
Now find r, and with that, get u1
hint: 64/625 = 4^3/(5^3 * 5)