i = p * r * n
i is the interest
p is the principal
r is the interest rate per time period
n is the number of time periods.
in your problem:
i = 900
p = 2000
r = what you want to find
n = 3 years
formula becomes 900 = 2000 * r * 3
solve for r to get r = 900 / 2000 / 3 = .15
that's .15 interest rate per year = 15% per year.
at a nominal interest rate of .15 per year, the interest rate per month would be .15/12 = .0125 per month.
the remaining balance at the end of 6 month is equal to 1907.140183
