A barrel of oil is used (1/5) for the first time, 25% is used for the second time, 20 kg is used for the third time, and 5 kg is left. How many kilograms is this barrel of oil originally?
一桶油第一次用去(1/5)，第二次用去25%，第三次用去20千克，还剩5千克．这桶油原来有多少千克？
<gadget id="calculator">20 + 5</gadget>
<output>25</output>

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

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/5) - (1/4)</gadget>
<output>11/20 = around 0.55</output>

<gadget id="calculator">25 / (11/20)</gadget>
<output>500/11 = around 45.454545</output>

<result>500/11 = around 45.454545</result>