A piece of paper, write big characters (3/7), draw pictures (2/7), how much of this paper is left?
一张纸，写大字用去它的(3/7)，画画用去它的(2/7)，还剩下这张纸的几分之几？
<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

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

<gadget id="calculator">1 - (3/7) - (2/7)</gadget>
<output>2/7 = around 0.285714</output>

<result>2/7 = around 0.285714</result>