The school cafeteria bought some rice and used it on the first day (2/7) and on the second day (3/7). Do you know how much of this rice is left?
学校食堂买来一些大米，第一天用去(2/7)，第二天用去(3/7)．你知道这些大米还剩多少吗？
<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>