[tex]a) \: \frac{3}{4} + \frac{5}{6} = \frac{9}{12} + \frac{10}{12} = \frac{19}{12} = 1 \: \frac{7}{12} [/tex]
[tex]b) \: \frac{17}{21} - \frac{3}{14} = \frac{34}{42} - \frac{9}{42} = \frac{25}{42} [/tex]
[tex]c) \: \frac{5}{6} - \frac{4}{15} = \frac{25}{30} - \frac{8}{30} = \frac{17}{30} [/tex]
