A and B have two piles of coal, take out (1/4) from A and give to B, then the two piles of coal are equal, the original mass of coal in B pile is as much as that of A
甲、乙两堆煤，从甲中取出(1/4)给乙，这时两堆煤就相等，原来乙堆煤的质量是甲的多少
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/4) * 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>