A piece of rope was used for the first time (1/3), but less (2/7) of the rope was used than the second time, what fraction of the rope was used for the second time?
一根绳子，第一次去用了(1/3)，比第二次少用了这根绳子的(2/7)，第二次用了这根绳子的几分之几？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

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

<gadget id="calculator">(1/3) + (2/7)</gadget>
<output>13/21 = around 0.619048</output>

<result>13/21 = around 0.619048</result>