A piece of cake, mother ate all (2/7), father ate all (3/7), how much of this cake is left?
一块蛋糕，妈妈吃了全部的(2/7)，爸爸吃的全部的(3/7)，这块蛋糕还剩下几分这几？
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

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

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