Tommy has 13 items in his pencil case. The pens are twice as many as the pencils and there's one eraser. How many pencils are there?
There are 13 items - 1 eraser = 
<gadget id="calculator">13-1</gadget>
<output>12</output>
12 pens and pencils.
There are 12 items / 3 = 
<gadget id="calculator">12/3</gadget>
<output>4</output>
4 pencils.

<result>4</result>