If one wire is used for the first time (2/5), and the wire is used for the second time (2/7), how much of the wire is left.
第一次用去一根铁丝的(2/5)，第二次用去这根铁丝的(2/7)，还剩下这根铁丝的多少．
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">1 - (2/5) - (2/7)</gadget>
<output>11/35 = around 0.314286</output>

<result>11/35 = around 0.314286</result>