Studying's not all fun and games, but it helps when your professor has a sense of humor. I just came across one of my favorite tax powerpoint slides of the semester, which I will attempt to recreate here:
§ 453: Mr. Doyle buys your giant cat for 10% downpayment and installments over the next five years. How are you taxed?
Income each year = payment (*) (gross profit / total contract price)