A barrel of oil, 40% is used for the first time, and the remaining 50% is used for the second time. There is still 12 kilograms of oil in the barrel. How many kilograms of oil are in the barrel?
一桶油，第一次用去40%，第二次用去余下的50%，桶里还剩下油12千克，原来桶里装了多少千克的油？
<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

<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">12 / (1/2) / (3/5)</gadget>
<output>40</output>

<result>40</result>