A barrel of oil is 20 kilograms, and there is still (2/5) left after some of it is used up. How many kilograms are used?
一桶油20千克，用去一些后还剩下(2/5)．用去多少千克？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">20 * (3/5)</gadget>
<output>12</output>

<result>12</result>