10 kilograms of oil are sold (4/5), how many kilograms are left.
10千克的油，卖出(4/5)，还剩多少千克．
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">10 * (1/5)</gadget>
<output>2</output>

<result>2</result>