A pile of coal (9/5) tons is used up (1/5), how many tons are left.
一堆煤(9/5)吨，用去了(1/5)，还剩多少吨．
<gadget id="calculator">9 / 5</gadget>
<output>9/5 = around 1.8</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(9/5) * (4/5)</gadget>
<output>36/25 = around 1.44</output>

<result>36/25 = around 1.44</result>