Answer :
[tex]a)\\\\\frac{1}{6} + \frac{1}{6}=\frac{1+1}{6}=\frac{2}{6}=\frac{1}{3}\\\\ b)\\\\\frac{1}{4} +\frac{3}{8}=\frac{2}{8}+\frac{3}{8}=\frac{5}{8}\\\\c)\\\\\frac{2}{3} +\frac{5}{6}=\frac{4}{6} +\frac{5}{6}=\frac{4+5}{6}=\frac{9}{6}=1\frac{3}{6}=1\frac{1}{2}[/tex]
[tex]d)\\\\\frac{9}{21} +\frac{ 4}{7}=\frac{3}{7} +\frac{ 4}{7}=\frac{3+4}{7}=\frac{7}{7}=1\\\\ e)\\\\ 1\frac{3}{5} + \frac{1}{10 }=1\frac{6}{10} + \frac{1}{10 }=1\frac{6+1}{10}=1\frac{7}{10}[/tex]
[tex]f)\\\\ 1\frac{ 1}{4} + \frac{11}{12} =1\frac{ 3}{12} + \frac{11}{12}=1\frac{3+11}{12} =1\frac{14}{12}=2\frac{2}{12}=2\frac{1}{6}\\\\g)\\\\ 1\frac{2}{3} + \frac{2}{3}=1\frac{2+2}{3}=1\frac{4}{3}=2\frac{1}{3}[/tex]
[tex]h)\\\\ 1\frac{5}{6} + 3 \frac{2}{5}=1\frac{5\cdot 5}{30} + 3 \frac{6\cdot 2}{30}=1\frac{25}{30} + 3 \frac{ 12}{30}=4\frac{25+12}{30}=4\frac{37}{30}=5\frac{7}{30}[/tex]
[tex]d)\\\\\frac{9}{21} +\frac{ 4}{7}=\frac{3}{7} +\frac{ 4}{7}=\frac{3+4}{7}=\frac{7}{7}=1\\\\ e)\\\\ 1\frac{3}{5} + \frac{1}{10 }=1\frac{6}{10} + \frac{1}{10 }=1\frac{6+1}{10}=1\frac{7}{10}[/tex]
[tex]f)\\\\ 1\frac{ 1}{4} + \frac{11}{12} =1\frac{ 3}{12} + \frac{11}{12}=1\frac{3+11}{12} =1\frac{14}{12}=2\frac{2}{12}=2\frac{1}{6}\\\\g)\\\\ 1\frac{2}{3} + \frac{2}{3}=1\frac{2+2}{3}=1\frac{4}{3}=2\frac{1}{3}[/tex]
[tex]h)\\\\ 1\frac{5}{6} + 3 \frac{2}{5}=1\frac{5\cdot 5}{30} + 3 \frac{6\cdot 2}{30}=1\frac{25}{30} + 3 \frac{ 12}{30}=4\frac{25+12}{30}=4\frac{37}{30}=5\frac{7}{30}[/tex]