[tex]2\frac{2}{7}-1\frac{1}{3}\\\\find\ LCD(\frac{2}{7};\frac{1}{3})\\\\the\ list\ of\ multiples\ of\ 7:\ 0;\ 7;\ 14;\ \fbox{21};\ 28;...\\the\ list\ of\ multiples\ of\ 3:\ 0;\ 3;\ 6;\ 9;\ 12;\ 15;\ 18;\ \fbox{21};\ 24;...\\\\LCD(\frac{2}{7};\ \frac{1}{3})=21\\\\\frac{2}{7}=\frac{2\times3}{7\times3}=\frac{6}{21}\\\frac{1}{3}=\frac{1\times7}{3\times7}=\frac{7}{21}\\-------------------[/tex]
[tex]2\frac{2}{7}-1\frac{1}{3}=2\frac{6}{21}-1\frac{7}{21}=1\frac{21+6}{21}-1\frac{7}{21}=1\frac{27}{21}-1\frac{7}{21}=\boxed{\frac{20}{21}}[/tex]
