How long will it take to save $4500 for a down payment on a new car if you make deposits of $250 every 3 months into account yielding 5.3% compounding quarterly?
Let's check your balance P after every quarter (3 months). Here is the table. The quarterly rate is r = 5.3%/4 = 0.01325
This provides an example of working with compound interest to determine how long it will take to save money.