The school bought 5 boxes of badminton, each with 12 pieces. 20 are used up, how many are left?
学校买来5盒羽毛球，每盒12只．用去20只，还剩下多少只？
<gadget id="calculator">12 * 5</gadget>
<output>60</output>

<gadget id="calculator">60 - 20</gadget>
<output>40</output>

<result>40</result>