### Instruction: 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?### Response: They sold 40 erasers because 20 x 2 = 40
They earned $40 from erasers because 80 - 40 = 40
One eraser costs $1 because 40 / 40 = 1
The answer is 1