There is a barrel of oil, the first time it is taken out (2/5), and the second time it is taken out (1/3), there is still 20 kilograms in the barrel, how many kilograms is the oil in the barrel.
有一桶油，第一次取出(2/5)，第二次取出(1/3)，桶里还剩20千克，这桶油原来有多少千克．
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (2/5) - (1/3)</gadget>
<output>4/15 = around 0.266667</output>

<gadget id="calculator">20 / (4/15)</gadget>
<output>75</output>

<result>75</result>