Use a batch of paper to bind exercise books of the same size. If each book has 16 pages, 400 copies can be bound. If each book has 20 pages, how many books can be bound less.
用一批纸装订同样大小的练习本，如果每本16页，可装订400本．如果每本20页，可以少装订多少本．
<gadget id="calculator">400 / 20</gadget>
<output>20</output>

<gadget id="calculator">16 * 20</gadget>
<output>320</output>

<gadget id="calculator">400 - 320</gadget>
<output>80</output>

<result>80</result>