math
posted by Tracy .
Saving for retirement by contributing the same amount each month from your 23rd birthday until your 65th birthday, in an account that pays a steady 4% annual interest compounded monthly.
How much will be in your fund at age 65 if you save $100 a month?

monthly rate = .04/12 = .003333...
time from 23rd to 65th birthday = 504 months
amount = 100( 1.003333..^504  1)/.003333..
= $130,517.61