A pile of coal is (3/4) tons, and (1/4) tons are used for the first time, how many tons are left.
一堆煤为(3/4)吨，第一次用去(1/4)吨，还剩多少吨．
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(3/4) - (1/4)</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>