Question

find annual interest rate I = $18, P= 200 t = 18 months

Answer 1

$Annual\: rate=\: 6\%\: or\: 0.06$

1) Since we have only this information, we can make use of the interest formula:

$I=Prt$

Note that we're going to find the rate per year, so we need to make a little adjustment since the period has been given in months:

$\frac{18}{12}=1.5$

2) Now, we can plug the data into the formula:

$\begin{gathered} I=Prt \\ 18=200r1.5 \\ 18=300r \\ 300r=18 \\ \frac{300r}{300}=\frac{18}{300} \\ r=0.06 \end{gathered}$

So, the annual rate is 6%