A pile of coal, 30% has been used up, how much of this pile of coal is left
一堆煤，用去了30%，还剩这堆煤的多少
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (3/10)</gadget>
<output>7/10 = around 0.7</output>

<result>7/10 = around 0.7</result>