The total amount due after a given period of time is given by the following formula:
This is for simple interest. <em>A</em> is the total amount due. <em>t</em> is the period of time, <em>r</em> is the interest rate and <em>P</em> is the initial amount borrowed.
To use the formula, <em>t</em> and <em>r</em> must have the same unit of time (both in years or both in months for example). We have the yearly rate as 15%, or well, 0.15. The period is 6 months, which will be half a year, or well, 0.5 years. With this information, we can now replace the values on the formula:
With this, the total amount due will be $3225.
Alternatively, we can first calculate the interest due with the following formula:
And add this amount to the initial amount of money borrowed to estimate the total amount due.
After six months, the student has to pay the $3000 borrowed, plus $225 of interest:
Answer. Total amount due after 6 months: $3225.