There is a rope, the full length (1/7) is used for the first time, and the full length (2/5) is left after a part is used for the second time. What fraction of the total length is used for the second time?
有一根绳子，第一次用去全长的(1/7)，第二次用去一部分后还剩全长的(2/5)．第二次用去全长的几分之几？
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(1/7) + (2/5)</gadget>
<output>19/35 = around 0.542857</output>

<gadget id="calculator">1 - (19/35)</gadget>
<output>16/35 = around 0.457143</output>

<result>16/35 = around 0.457143</result>