For a barrel of oil, 40% of the oil is poured out for the first time, and 10 kg less than the first time is poured out for the second time, and there is still 30 kg in the barrel. How many kilograms of oil is there in the barrel?
一桶油，第一次倒出40%，第二次比第一次少倒出10千克，桶里还剩30千克，这桶油原来有多少千克．
<gadget id="calculator">30 - 10</gadget>
<output>20</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5) - (2/5)</gadget>
<output>1/5 = around 0.2</output>

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

<result>100</result>