Kindergarten buys back some toys, distributes them to the children in the small class (2/7), distributes them to the children in the middle class (4/7), and gives the rest to the big class. How much do the children in the big class get?
幼儿园买回一些玩具，发给小班的小朋友(2/7)，发给中班的小朋友(4/7)，剩下的给大班．大班的小朋友分到几分之几？
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">1 - (2/7) - (4/7)</gadget>
<output>1/7 = around 0.142857</output>

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