3. if the typical balance on lucy's credit card is $650 and the interest rate (apr) on her credit card is 18%, how much in interest would you expect lucy to be charged in a typical month?

First we convert the percentage to a decimal number.  18% means 18 out of 100, so 18/100 = 0.18.  Since this is a yearly percentage and we want a monthly, we then divide this by 12.  0.18/12 = 0.015.  Next we multiply her typical balance, $650, by this decimal.  650(0.015)=$9.75 in interest for that month.