A pile of coal, (2/3) is used, and ((())/(())) is left; a truckload of cement weighs 4 tons, and (3/5) is used, how many tons are left.
一堆煤，用去(2/3)，还剩((())/(()))；一车水泥重4吨，用去(3/5)，还剩多少吨．
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 - (2/3)</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 / (1/3) / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">4 * (2/5)</gadget>
<output>8/5 = around 1.6</output>

<result>8/5 = around 1.6</result>