Originally Posted by

**Reckoner** If you know the formula, it should be fairly simple. Just substitute in the appropriate values, and solve for the unknown.

For example, for number 1, you should have

$\displaystyle A = P\left(1 + \frac r n\right)^{nt}$

$\displaystyle \Rightarrow10775.64 = P\left(1+\frac{0.08}{12}\right)^{12\cdot50}$

Solve for the principle $\displaystyle P$.

For number 2, subtract the present value from the future value to get the interest paid, and for number 3, just substitute and solve for $\displaystyle r$.