A cart of chemical fertilizers was transported away for the first time (1/7), and for the second time (3/7). How much of the total was transported twice?
一车化肥，第一次运走了(1/7)，第二次运走了(3/7)．两次一共运走了几分之几？
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">(1/7) + (3/7)</gadget>
<output>4/7 = around 0.571429</output>

<result>4/7 = around 0.571429</result>