human
David found $12 on the street. He then gave it to his friend Evan who has $1 and needed to buy a watch worth $20. How much does Evan still need?
assistant
How much money does Evan have? ** The total amount Evan has is $1 + $12 = $<<1+12=13>>13.
How much does Evan still need? ** So Evan still needs $20 - $13 = $<<20-13=7>>7.
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