# How long will a $9000 investment take to earn$180 interest at an annual interest rate of 8%?

May 11, 2018

$t$ = $0.25$ years

#### Explanation:

Simple Interest

$I = p r t$

$I$: interest ($180) $p$: principal ($9000)
$r$: rate (8%, $\frac{8}{100}$ , becomes $.08$)
$t$: time (unknown, in years)

$180$ = $\left(9000\right)$$\left(.08\right)$$\left(t\right)$

First, multiply 9000 by .08 to simplify in order to isolate for t.

$9000 \cdot .08$ = 720

$180$ = $720$$\left(t\right)$

Divide 180 by 720 to isolate for t.

$t = 0.25$ yrs , or 3 months