A bundle of wires is used up (2/7) for the first time and (3/7) for the second time, how much is left?
一捆电线，第一次用去(2/7)，第二次用去(3/7)，还剩下几分之几？
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">1 - (2/7) - (3/7)</gadget>
<output>2/7 = around 0.285714</output>

<result>2/7 = around 0.285714</result>