There are (4/5) tons of coal in a pile, and (1/4) is used up, how much of this pile of coal is left
一堆煤有(4/5)吨，用去了(1/4)，还剩这堆煤的多少
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<result>3/4 = around 0.75</result>