1 ton of coal, (1/4) ton is used, how many tons of coal are left.
1吨煤，用去(1/4)吨，还剩多少吨煤．
<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>