20 tons of coal are used (4/5), how many tons of coal are used.
20吨煤，用去(4/5)，用去多少吨煤．
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">20 * (4/5)</gadget>
<output>16</output>

<result>16</result>