A cart of chemical fertilizers was transported away for the first time (2/7), and for the second time (3/7). How much of the total was transported twice? What fraction is left?
一车化肥，第一次运走了(2/7)，第二次运走了(3/7)．两次一共运走了几分之几？还剩几分之几？
<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">(2/7) + (3/7)</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">1 - (5/7)</gadget>
<output>2/7 = around 0.285714</output>

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