If (3/7) of a steel bar is used up, what fraction of the total length is left over the used one?
一根钢筋用去了它的(3/7)，剩下的比用去的多全长的几分之几？
<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">1 - (3/7) - (3/7)</gadget>
<output>1/7 = around 0.142857</output>

<result>1/7 = around 0.142857</result>