Dongdong's father and mother each ate a watermelon (2/7), and Dongdong ate the rest. How much of the watermelon did Dongdong eat?
东东的爸爸、妈妈各吃了一个西的瓜(2/7)，剩下的东东吃了，东东吃了这个西瓜的几分之几？
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">1 - (2/7) - (2/7)</gadget>
<output>3/7 = around 0.428571</output>

<result>3/7 = around 0.428571</result>