20 table tennis balls, take away (1/5), how many are left.
20个乒乓球，拿走它的(1/5)，还剩多少个．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">20 * (1/5)</gadget>
<output>4</output>

<gadget id="calculator">20 - 4</gadget>
<output>16</output>

<result>16</result>