Pia's shiny bikePia wanted a shiny forty-coin bike and the shop took the card, so the bank paid the shop and forty coins were owed to the bank. In this pretend town the bank adds an extra coin per full ten owed, so forty owed has four full tens and adds four extra a month. A month later a statement came: forty owed plus four extra made forty-four, and at the bottom it said, "Minimum payment: five coins." Five was much smaller than forty-four, so Pia could pay with ease, and the minimum is the least the bank will accept this month. Look where the five coins went: four of them paid the month's extra, and only one was left to cut the forty, so now Pia owed thirty-nine. Next month thirty-nine owed had three full tens, so the extra was three and the minimum four, and after paying it Pia owed thirty-eight. The balance crept down like a snail down a staircase, one coin a month, and at that speed forty coins take forty months. All that time the extra coins kept coming, so added up, Pia paid one hundred four coins for a bike that cost forty. Paying twelve coins every month instead, Pia is free in five months, which is fifty coins in all, for the same bike! A minimum payment is a gate, not a finish line, because it says what the bank accepts this month, not when the debt ends.