Mom cuts a piece of cake, Wenwen eats the whole cake (4/7), after mom eats, there is still the whole cake (1/7). What fraction of the whole cake did mom eat?
妈妈切开一块蛋糕，文文吃了整块蛋糕的(4/7)，妈妈吃了以后，还剩整块蛋糕的(1/7)．妈妈吃了整个蛋糕的几分之几？
<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">1 - (4/7) - (1/7)</gadget>
<output>2/7 = around 0.285714</output>

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