A project, A has done its (2/7), B has done its (1/3), A and B have done a total of how much of the whole project.
一项工程，甲做了它的(2/7)，乙做了它的(1/3)，甲乙两队共做了全工程的多少．
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(2/7) + (1/3)</gadget>
<output>13/21 = around 0.619048</output>

<result>13/21 = around 0.619048</result>