A rope is 20 meters long, after how many meters are cut off, the rest accounts for 40% of the total length.
一根绳子长20米，剪去多少米后，剩下的占全长的40%．
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">20 * (3/5)</gadget>
<output>12</output>

<result>12</result>