Paul got a box of 521 crayons and 66 erasers for his birthday. At the end of the school year he only had 154 left while not having lost a single erasers. How many crayons had been lost or given away?
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First, we know that Paul had 521 crayons at the beginning of the school year. 

Then, we know that at the end of the school year, he had 154 crayons left. 

That means that he lost or gave away 367 crayons.