Question

You ran a little short on your spring break vacation, so you put $1,000 on your credit card. you can only afford to make the minimum payment of $20 per month. the interest rate on the credit card is 1.5 percent per month. how long will you need to pay off the$1,000? how much interest will you pay?

Answer 1

 Use the PV of an Annuity tables, where PV is $1,000, Annuity is $20, and Rate is 1.5%. But remember that the equation for this table is PV = Annuity x Factor. Since we know the PV and the Annuity, solve for the Factor. 

PV / Annuity = Factor, so $1,000 / $20 = 50 (the Factor). From the table, find where a Factor of 50 meets a rate of 1.5%. A factor of 49.9724 appears at 1.5% and 93 Periods. 

The formula for the PV of an Annuity is (1 - 1 / (1 + r)^n) / r. So 1,000 = (1 - 1 /(1.015)^n / .015. 
To solve for n gets too difficult