## Thinking Mathematically (6th Edition)

The time required for an amount of money to double in value is given by $t = \frac{1}{r}$
This is the formula we use when we make calculations with simple interest: $A = P~(1+rt)$ $A$ is the future value $P$ is the present value $r$ is the interest rate $t$ is the number of years Let's suppose that the future value is $2P$. We can find the time $t$ that is required to reach this future value. $A = P~(1+rt)$ $2P = P~(1+rt)$ $2 = 1+rt$ $rt = 1$ $t = \frac{1}{r}$ The time required for an amount of money to double in value is given by $t = \frac{1}{r}$