初中maths - compound interest

Principal=$9600, interest rate=4% p.a. compounded monthly, period=3 years
Find the amount and compound interest.

Then, the interest rate per month = 4% / 12 = (1/3)% as the p.a. (per annum) interest rate is 4%. The number of periods compounded, n = 3 * 12 = 36 as there are 12 months in a year.

By the formula for calculating the amount of compound interest, amount A = P(1 + r%)^n , we have A = 9600[1 + (1/3)%]^36 = 10821.81 (to 2 d.p.)

Interest I = A - P = 10821.81 - 9600 = 1221.81 (to 2 d.p.)

Please feel free to ask if you don't understand or there are any mistakes.