pile of coal, 40% of the total amount is used on the first day, and the remaining 40% is used on the second day, how much of the total amount is left in this pile of coal
一堆煤，第一天用去总量的40%，第二天用去余下的40%，这堆煤还剩下总量的多少
<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) * (3/5)</gadget>
<output>9/25 = around 0.36</output>

<result>9/25 = around 0.36</result>