brain is shutting down need help

Question

You deposit $300 each month into an account earning 5% interest compounded monthly.

a) How much will you have in the account in 20 years?

b) How much total money will you put into the account?

c) How much total interest will you earn?

Answer 1

a) In financial calculator, all expressed on monthly basis:

PMT = 300

I = 5/12 = .4167 (assumed yearly, converted to monthly)

N = 240 months

FV = $123,310.10

b) Deposits made = $300/mo for 240 months = $72,000

c) Interest earned = FV - deposits made = $51,310.10

I am assuming the 5% stated rate is an annual rate, not monthly. If we plug in 5% as a monthly rate we end up with a 9 figure future value. Please let me know if you need any further explanation.