A barrel of oil weighs 60.2kg. After half of the oil is used, the weight of the barrel is 31.8kg. How many kilograms does the oil barrel weigh?
一桶油连桶重60.2kg，用去一半油后，连桶重31.8kg，油桶重多少千克．
<gadget id="calculator">60.2 - 31.8</gadget>
<output>28.4</output>

<gadget id="calculator">28.4 * 2</gadget>
<output>56.8</output>

<gadget id="calculator">60.2 - 56.8</gadget>
<output>3.4</output>

<result>3.4</result>