A rope is (7/5) meters long, (1/2) of the total length is used for the first time, and (2/7) is used for the second time, what fraction of the rope is useless?
一根绳长(7/5)米，第一次用去总长度的(1/2)，第二次又用去(2/7)，这根绳还剩几分之几没有用？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

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

<gadget id="calculator">1 - (1/2) - (2/7)</gadget>
<output>3/14 = around 0.214286</output>

<result>3/14 = around 0.214286</result>