A barrel of oil weighs 27 kg even after 20% is used. After using (1/2), the barrel weighs 18 kg in total. How many kilograms is this barrel of oil originally?
一桶油，用去20%后连桶重27千克．用去(1/2)后连桶共重18千克．这桶油原来有多少千克？
<gadget id="calculator">27 - 18</gadget>
<output>9</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/2) - (1/5)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">9 / (3/10)</gadget>
<output>30</output>

<result>30</result>