If you take out (1/5) of the oil from barrel A and pour it into barrel B, then the two barrels of oil are the same weight, how much more barrel A is than barrel B
如果从甲桶油取出(1/5)倒入乙桶油，这时两桶油就同样重，原来甲桶比乙桶多多少
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5) - (1/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>