[tex] \frac{1}{2} + \frac{3}{5} + \frac{2}{7} = \\ \\ \frac{1 \times 35}{2 \times 35} + \frac{3 \times 14}{5 \times 14} + \frac{2 \times 10}{7 \times 10} = \\ \\ \frac{35}{70} + \frac{42}{70} + \frac{20}{70} = \\ \\ \frac{35 + 42 + 20}{70} = \frac{97}{70} [/tex]
