Jack bought 3 books a month at $20 each.  He sells them back at the end of the year for $500.  How much money did he lose?
He bought 3*20=$<<3*20=60>>60 of books a month
That means he bought 60*12=$<<60*12=720>>720 of books a year
So he lost 720-500=$<<720-500=220>>220
#### 220