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

# Answer

220
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
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?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
220
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?
train