A pile of coal weighs 13.5 tons, has been used (4/9), how many tons are left.
一堆煤重13.5吨，已经用去(4/9)，还剩多少吨．
<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">1 - (4/9)</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">13.5 * (5/9)</gadget>
<output>7.5</output>

<result>7.5</result>