Think about it, a rope is 1 meter long, first cut off 40 cm, and then cut off 20 cm, how many centimeters are left?
想一想，一根绳子，长1米，先剪去40厘米，又剪去20厘米，还剩多少厘米？
<gadget id="calculator">1 * 100</gadget>
<output>100</output>

<gadget id="calculator">100 - 40 - 20</gadget>
<output>40</output>

<result>40</result>