pile of 15 tons of coal, take away (1/5), how many tons are left.
一堆煤15吨，运走它的(1/5)，还剩多少吨．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">15 * (1/5)</gadget>
<output>3</output>

<gadget id="calculator">15 - 3</gadget>
<output>12</output>

<result>12</result>