Multiple choice general knowledge The APR of a variable-rate credit card can be based on which of these indexes? The Prime rate The three-month Treasury Bill rate The Federal Reserve Discount rate Any of the above Reveal answer Fill a bubble to check yourself D Correct answer Explanation Variable APRs can be pegged to various benchmark rates including Prime, Treasury Bill, or Federal Reserve Discount rates. The card agreement specifies which index plus margin are used, so all three are valid bases for determining your rate.