There is a pile of 20 tons of coal, which is transported away (2/5), how many tons are left.
有一堆煤20吨，运走了(2/5)，还剩多少吨吨．
<gadget id="calculator">2 / 5</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>