Revisiting Compound Interest Formula:
The amount of money, A, that a principal, P, will grow to after t years at interest rate r (convert
the rate to decimal form), compounded n times per years is given by the formula
$A = P\left(1 + \frac{r}{n}\right)^{nt}$
Ex. 7 Suppose that $3,000 is invested at 3% interest compounded monthly. How long would it
take the amount to reach $4,000?