A barrel of oil is taken out (7/10), and then 10 kilograms are put in. At this time, the oil in the barrel is equal to the original (2/5), how much oil is in the original barrel?
一桶油取出(7/10)，再放入10千克，这时桶里的油等于原来的(2/5)，原来桶里有多少油？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">7 / 10</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">1 - (7/10)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">(2/5) - (3/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">10 / (1/10)</gadget>
<output>100</output>

<result>100</result>