John buys 3 boxes of burritos.  He gives away a 3rd of them to his friend.  Each box has 20 burritos.  He eats 3 burritos per day for 10 days.  How many burritos does he have left?
He gave 3/3=
<gadget id="calculator">3/3</gadget>
<output>1</output>
1 box away.
So he has 3-1=
<gadget id="calculator">3-1</gadget>
<output>2</output>
2 boxes.
So he got 2*20=
<gadget id="calculator">2*20</gadget>
<output>40</output>
40 burritos.
He ate 3*10=
<gadget id="calculator">3*10</gadget>
<output>30</output>
30 burritos.
So he has 40-30=
<gadget id="calculator">40-30</gadget>
<output>10</output>
10 burritos left.

<result>10</result>