posted by Marquita .
David would like to buy a laptop computer and save 20 percent during sale. He uses his credit card to pay for it. David is counting on getting a lot of money in graduation presents from his parents' business associates. David knows that his credit card company offers a 28 day grace period, so if he pays off the whole amount, he won't owe any interest. Sure enough, after his big party, David counts up the checks and has 1000! When he gets his credit card bill at the end of the month, he is able to pay the balance of 800 in full
How long will it take for David to pay off the 800?
How much interest will he have to pay ?