[tex]a) \frac{5}{12} + \frac{9}{12} = \frac{5 + 9}{12} = { \frac{14}{12} }^{(2} = \frac{7}{6} = 1 \frac{1}{6} [/tex]
[tex]b) \frac{4}{15} - \frac{7}{15} = \frac{4 - 7}{15} = - \frac{3}{15} ^{(3} = - \frac{1}{5} [/tex]
[tex]c) \frac{2}{21} + \frac{1}{7} = \frac{2}{21} + \frac{1 \times 3}{7 \times 3} = \frac{2}{21} + \frac{3}{21} = \frac{2 + 3}{21} = \frac{5}{21} [/tex]
[tex]d) \frac{3}{16} - \frac{9}{24} = \frac{3 \times 3}{16 \times 3} - \frac{9 \times 2}{24 \times 2} = \frac{9}{48} - \frac{18}{48} = \frac{9 - 18}{48} = - { \frac{9}{48} }^{(3} = - \frac{3}{16} [/tex]
[tex]e) - \frac{7}{9} + \frac{8}{10} = \frac{ - 7 \times 10}{9 \times 10} + \frac{8 \times 9}{10 \times 9} = - \frac{70}{90} + \frac{72}{90} = \frac{ - 70 + 72}{90} = { \frac{2}{90} }^{(2} = \frac{1}{45} [/tex]
[tex]f) - \frac{11}{12} - 1 \frac{2}{5} = \\ \\ 1 \frac{2}{5} = \frac{1 \times 5 + 2}{5} = \frac{5 + 2}{5} = \frac{7}{5} \\ \\ - \frac{11}{12} - \frac{7}{5} = \frac{ - 11 \times 5}{12 \times 5} - \frac{7 \times 12}{5 \times 12} = - \frac{55}{60} - \frac{84}{60} = \frac{ - 55 - 84}{60} = - \frac{139}{60} = - 2 \frac{19}{60} [/tex]
