A rope is cut twice in a row, and (3/7) of it is cut each time. By how much is the rope shorter?
一根绳子，连续剪去两次，每次剪去它的(3/7)，这根绳子短了几分之几？
<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">(3/7) + (3/7)</gadget>
<output>6/7 = around 0.857143</output>

<result>6/7 = around 0.857143</result>