After 20% of a barrel of oil is used up, another 15 kilograms is poured in. At this time, the oil is less than the original (1/20), how many kilograms is the original barrel of oil?
一桶油，用去20%后，又倒进15千克，这时的油比原来少(1/20)，这桶油原有多少千克？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

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

<gadget id="calculator">15 / (3/20)</gadget>
<output>100</output>

<result>100</result>