You need to borrow $200 for 60 days. Is it cheaper to do so for a flat $10 fee on repayment or by using a credit card with an APR of 20% (compounded monthly)?
I can't do the math to answer this question in my head. I suspect you can't either. The point of normalizing the cost of borrowing money to an APR is so that a consumer can make this decision without having to solve exponential equations.