There is a barrel of oil, 20% is used for the first time, and (2/5) kg is used for the second time, and 3.4 kg is used for the two times. How much does this barrel of oil weigh?
有一桶油，第一次用去20%，第二次又用去(2/5)千克，两次一共用去3.4千克．这桶油重多少千克．
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">3.4 - (2/5)</gadget>
<output>3</output>

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

<gadget id="calculator">3 / (1/5)</gadget>
<output>15</output>

<result>15</result>