(1/5) of an iron wire is used up, and (1/5) meter is left, how many meters is this iron wire long?
一根铁丝用去(1/5)，还剩(1/5)米，这根铁丝长多少米．
<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">(1/5) / (4/5)</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>