# Sandra invests $5,000 in a savings account that pays 5% simple interest. How many years will it take for the account to grow to$15,000, if she makes no withdrawals or deposits?

$40 \text{ }$years
The formula for SI is: $S I = \frac{P R T}{100}$
To have an account of $15,000" "(A) means that she needs to have earned $10,000 interest on her investment of $5,000" "(P) In simple interest, interest is calculated only on the initial amount. $S I = \frac{P R T}{100} = 10000$$\frac{5000 \times 5 \times \textcolor{b l u e}{T}}{100} = 10000$$\textcolor{b l u e}{T} = \frac{10000 \times 100}{5000 \times 5}$$T = 40$years $\rightarrow\$ No one would invest at simple interest!