(1/7) of a piece of paper is painted red, (2/7) is painted black, and the rest is painted green, what fraction of the paper is painted green?
一张纸的(1/7)涂红色，(2/7)涂黑色，剩下的涂绿色，涂绿色的是这张纸的几分之几？
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

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

<gadget id="calculator">1 - (1/7) - (2/7)</gadget>
<output>4/7 = around 0.571429</output>

<result>4/7 = around 0.571429</result>