For a wire, use the full length (2/5) for the first time, and use the remaining (4/5) for the second time. Full length ((())/(())) left.
一根电线，第一次用去全长的(2/5)，第二次用去余下的(4/5)．还剩全长的((())/(()))．
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(3/5) * (4/5)</gadget>
<output>12/25 = around 0.48</output>

<gadget id="calculator">1 - (2/5) - (12/25)</gadget>
<output>3/25 = around 0.12</output>

<result>3/25 = around 0.12</result>