Answer
$\frac{2}{3}$
Work Step by Step
$\frac{2}{7}+\frac{8}{21}$
$=\frac{2\times3}{7\times3}+\frac{8\times1}{21\times1}$
$=\frac{6}{21}+\frac{8}{21}$
$=\frac{14}{21}$
$=\frac{2}{3}$
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