A pile of coal, 40% is used, how much is the rest
一堆煤，用了40%，剩下的占用去的多少
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

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

<gadget id="calculator">(3/5) / (2/5)</gadget>
<output>3/2 = around 1.5</output>

<result>3/2 = around 1.5</result>