A pile of 16 tons of coal is used up (1/4), how many tons are left?
一堆煤16吨，用去(1/4)，还剩多少吨．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">16 * (1/4)</gadget>
<output>4</output>

<gadget id="calculator">16 - 4</gadget>
<output>12</output>

<result>12</result>