Each schoolbag retails for 25 yuan, wholesale buy 4 get one free. How much is the average wholesale price?
书包每只零售25元，批发买4只送一只．按批发价平均每只只需多少钱？
<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">25 * (4/5)</gadget>
<output>20</output>

<result>20</result>