A barrel of gasoline, after 40% is used, the remaining weight is 20 kg more than the used weight, how many kg is used?
一桶汽油，用去40%后，剩下的重量比用去的重量多20千克，用去多少千克？
<gadget id="calculator">40 / 100</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">(3/5) - (2/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">20 / (1/5)</gadget>
<output>100</output>

<gadget id="calculator">100 * (2/5)</gadget>
<output>40</output>

<result>40</result>