[tex]a) \frac{3}{4} - \frac{1}{2} = \frac{3}{4} - \frac{1 \times 2}{2 \times 2} = \frac{3}{4} - \frac{2}{4} = \frac{3 - 2}{4} = \frac{1}{4} [/tex]
[tex]b) \frac{5}{6} + \frac{1}{4} = \frac{5 \times 2}{6 \times 2} + \frac{1 \times 3}{4 \times 3} = \frac{10}{12} + \frac{3}{12} = \frac{10 + 3}{12} = \frac{13}{12} = 1 \frac{1}{12} [/tex]