Using the equation at the top … I=Prt … You know the principal ($500) but you don’t know the time or interest rate. If the rate is only 1%, then you owe them $505, and you can pay that off in. (505/84 = 6.01) about 6 months. If the rate is 200%, then you have to keep paying $84 every month for as long as you live, and at the end, you still owe them $500. So the time it takes to pay it off depends on the interest rate, which you’ll have to ask WalMart. / / / The pro to buying on credit and interest is that you always get the stuff you want when you want it, just like you did when you were 2 years old, and you never have to wait. The con is that you always pay more for it. You pay and pay and pay and pay, all for the permission to not pay yet for what you bought, while making somebody else rich. A pretty stupid choice when you think about it.