After using (1/7) of a rope, there is still (4/7) meters left, how much of this rope is left
一根绳子用去(1/7)后，还剩下(4/7)米，还剩下这根绳子的多少
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">1 - (1/7)</gadget>
<output>6/7 = around 0.857143</output>

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