Paul got a box of 12 crayons and 11 erasers for his birthday. At the end of the school year he only had 4 left while not having lost a single erasers. How many crayons had been lost or given away?
Paul got a box of 12 crayons and 11 erasers for his birthday. 

At the end of the school year he only had 4 left while not having lost a single erasers. 

How many crayons had been lost or given away?

We know that Paul had 4 crayons left at the end of the school year, and we know that he did not lose any erasers. So, we can infer that he must have given away or lost 8 crayons.