Tim won a $100 raffle.  He gave away 20% to his friend.  How much did he keep?
He gave away 100*.2=$
<gadget id="calculator">100*.2</gadget>
<output>20</output>
20.
So he kept 100-20=$
<gadget id="calculator">100-20</gadget>
<output>80</output>
80.

<result>80</result>