For a full barrel of oil, use up (1/4) of the barrel for the first time, and use the rest (1/5) for the second time. The first time uses 2kg more than the second time, how much does this barrel of oil weigh?
一满桶油，第一次用去这桶油的(1/4)，第二次用剩下的(1/5)．第一次比第二次多用去2kg，这桶油重多少千克？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(3/4) * (1/5)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">(1/4) - (3/20)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">2 / (1/10)</gadget>
<output>20</output>

<result>20</result>