Mark wants to tip his server 20% on a $200 check. If his friend agrees to kick in $10, how much should Mark add?
First find the total tip amount: 20% * $200 = $
<gadget id="calculator">20*.01*200</gadget>
<output>40</output>
40.
Then subtract the friend's contribution: $40 - $10 = $
<gadget id="calculator">40-10</gadget>
<output>30</output>
30.

<result>30</result>