Today I was watching my sister do her Financial homework and I tryed to do one of them problems it said something about haveing 5000 bucks at 9% interest for 6 years and you had to find how much you would have. And so I tryed to use the compound interest formula P=A(1+(r/n)^rt but we both got totaly different anwers. She did it on a standar issued financial caculator. So is that the formula for compound interest? P=A(1+(r/n)^rt. And is this how you plug it in? P=5,000(1+(.09/6)^(.09*6) Also what are other interest raletaed equations and state what goes in the variables. All the other ones that I know are: Compound Interest: P=A(1+(r/n)^rt Compound Interest Continusly: P=e^rt Rule of 72 Rule of 82 Simple Interest: You dont really need a formula for this one, all that happens is that your you only earn interest on your original amound earns interst.