What is used in a pile of coal is the rest (1/3), how much of the pile of coal is used.
一堆煤用去的是剩下的(1/3)，用去的占这堆煤的多少．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 + (1/3)</gadget>
<output>4/3 = around 1.333333</output>

<gadget id="calculator">(1/3) / (4/3)</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>