Take 20% of the oil from barrel A and pour it into barrel B, then the weight of the two barrels of oil in A and B is equal, and the original B is equal to the amount of A.
从甲桶油取出20%倒入乙桶，则甲乙两桶油重量相等，原乙相当于甲的多少．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<result>3/5 = around 0.6</result>