piece of cake, mom and dad each eat it (2/5), Xiaoshi eats up the rest, how much of the cake does Xiaoshi eat?
一块饼，爸爸妈妈各吃它的(2/5)，小诗把剩下的都吃完了，小诗吃了这个饼的几分之几？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) + (2/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<result>1/5 = around 0.2</result>