Jasmine invests a sum of money in a savings account with a fixed annual interest rate of 8% compounded continuously. After 9 years, the balance reaches $18,091.34. What was the amount of the initial investment?



Answer :

To calculate the accrued amount of an account that compounds continuously you have to apply the following formula:

[tex]A=Pe^{rt}[/tex]

Where

A is the accrued or final amount

P is the principal or initial amount

r is the interest rate expressed as a decimal value

t is the time period in years

You have to determine the principal amount given that after 9 years the final balance of an account that has an annual interest of 8% is $18,091.34

- The first step is to write the formula for the principal amount P, to do so, divide both sides of the expression by e^(rt)

[tex]\begin{gathered} \frac{A}{e^{rt}}=\frac{Pe^{rt}}{e^{rt}} \\ P=\frac{A}{e^{rt}} \end{gathered}[/tex]

- Next, divide the interest rate by 100 to express it as a decimal value

[tex]\begin{gathered} r=\frac{8}{100} \\ r=0.08 \end{gathered}[/tex]

- Now you can calculate the principal amount, replace the expression using A=18,091.34, r=0.08, and t=9

[tex]\begin{gathered} P=\frac{18091.34}{e^{0.08\cdot9}} \\ P=\frac{18091.34}{e^{0.72}} \\ P=8806.000558\cong8806.00 \end{gathered}[/tex]

The initial amount of the investment was $8806