8.3: A Personal Finance Example Using While Loops
A student decides to finance their college education using a credit card. They charge one semester's tuition and then make the minimum monthly payment until the credit card balance is zero. How many months will it take to pay off the semester's tuition? How much will the student have spent to pay off the tuition?
We can solve this problem using an mfile script. We define the following variables:

bn  Balance at monthn . 
Pn  Payment in monthn . 
fn  Finance charge (interest) in monthn .
The finance charge
Credit card interest rates are typically given as an annual percentage rate (APR). To convert the APR to a monthly interest rate, use the following formula:
More information on how to compute monthly rates can be found at the Wikipedia article "Credit card interest" (http://en.wikipedia.org/wiki/Credit_card_interest).
Credit cards usually have a minimum monthly payment. The minimum monthly payment is usually a fixed percentage of the balance; the percentage is required by federal regulations to be at least
To compute the balance for one month (month
In the following exercises, we will develop the program to compute the number of months necessary to pay the debt. We will assume that the card APR is
Exercise 5
Write code to compute the monthly interest rate
Exercise 6
Write code to compute the minimum monthly payment
Exercise 7
Write code to compute the balance at month
Exercise 8
Place the code developed for Exercise 7 into a while loop to determine how many months will be required to pay off the card.
Exercise 9
Modify your code from Exercise 8 to plot the monthly balance, monthly payment, and total costtodate for each month until the card is paid off.