A barrel of oil weighs 20 kilograms, use up (3/4), how many kilograms are left.
一桶油重20千克，用去(3/4)，剩下多少千克．
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

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

<result>5</result>