After using up 40% of a barrel of oil, pour another 2 liters into it, and then the oil in the barrel is as much as the original one. How many liters is this barrel of oil?
用去一桶油的40%后又倒入2升，这时桶里的油和原来的一样多．这桶油原有几升？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

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

<result>5</result>