The gasoline barrels weigh 20 kilograms in total, half of which is used first, and then the remaining half is used, and the barrels weigh 8 kilograms at this time. How many kilograms does the barrel weigh.
汽油连桶共重20千克，先用去一半，接着又用去剩下的一半，这时连桶重8千克．桶重多少千克．
<gadget id="calculator">20 - 8</gadget>
<output>12</output>

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

<gadget id="calculator">(1/2) * (1/2)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/2) + (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">12 / (3/4)</gadget>
<output>16</output>

<gadget id="calculator">20 - 16</gadget>
<output>4</output>

<result>4</result>