bundle of wires is 5 meters long, the first time uses up the full length (2/5), and the second time uses up the full length (1/4), what fraction of the full length is left?
一捆电线长5米，第一次用去全长的(2/5)，第二次用去全长的(1/4)，还剩下全长的几分之几？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(2/5) + (1/4)</gadget>
<output>13/20 = around 0.65</output>

<gadget id="calculator">1 - (13/20)</gadget>
<output>7/20 = around 0.35</output>

<result>7/20 = around 0.35</result>