Kim orders a $10 meal and a drink for 2.5.  She gives a 20% tip.  She pays with a $20 bill.  How much does she get in change?
The dinner cost 10+2.5=$
<gadget id="calculator">10+2.5</gadget>
<output>12.5</output>
12.5.
The tip comes to 12.5*.2=$2.5.
So the total cost is 12.5+2.5=$
<gadget id="calculator">12.5+2.5</gadget>
<output>15</output>
15.
That means she gets 20-15=$
<gadget id="calculator">20-15</gadget>
<output>5</output>
5 in change.

<result>5</result>