A store sells pencils and erasers. It has a rule that for every pencil you buy, you must buy 2 erasers which cost 1/2 the price of the pencils. If they sold 20 pencils and earned $80, how much do erasers cost?
They sold 40 erasers because 20 x 2 = 
<gadget id="calculator">20*2</gadget>
<output>40</output>
40.
Therefore 20(Pencil Price) + (1/2)(40 x Pencil Price) = 80.
Therefore 40(Pencil Price) = 80.
Therefore (Pencil Price) equals 2 because 80 / 40 = 
<gadget id="calculator">80/40</gadget>
<output>2</output>
2.
An eraser costs $1 because 2 / 2 = 
<gadget id="calculator">2/2</gadget>
<output>1</output>
1.

<result>1</result>