A pile of coal, 40% has been used, how much of this pile of coal is left
一堆煤，用了40%，还剩这堆煤的多少
<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>

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