After 40 tons of coal is increased by (1/5) tons, and then reduced by ((())/(())), it is still 40 tons.
40吨煤增加(1/5)吨后，再减少((())/(()))，还是40吨．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">40 + (1/5)</gadget>
<output>201/5 = around 40.2</output>

<gadget id="calculator">(1/5) / (201/5)</gadget>
<output>1/201 = around 0.004975</output>

<result>1/201 = around 0.004975</result>