Melissa used her credit card to buy a $745 refrigerator. She kept the refrigerator for exactly nine years, during which time it consumed an average of $0.19 of electricity every day. Melissa’s credit card has an APR of 16.84%, compounded monthly. Melissa paid off her refrigerator by making identical monthly payments for four years. If she made no other purchases with her card, what percentage of the lifetime cost of the refrigerator did the electricity make up? (Assume that two of the years were leap years, and round all dollar values to the nearest cent.)
The monthly interest rate is 0.1684 ÷ 12, and 48 equal monthly payments on a $745 balance are about $21.43 each. The total paid for the refrigerator is therefore about 48 × $21.43 = $1,028.64. Electricity costs $0.19 × (9 × 365 + 2) = $624.53; its share of the lifetime cost is $624.53 ÷ ($1,028.64 + $624.53) × 100 ≈ 37.77%, choice D.
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