A pile of coal, 30 tons are used up, and (1/3) is left, how many tons are there?
一堆煤，用去30吨，还剩(1/3)，原有多少吨．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">30 / (2/3)</gadget>
<output>45</output>

<result>45</result>