Решите примеры, используя наиболее удобный способ. 669.

Решение:

• \[ \frac{6}{7} + \frac{3}{5} + \frac{1}{7} + \frac{3}{5} = \left( \frac{6}{7} + \frac{1}{7} \right) + \left( \frac{3}{5} + \frac{3}{5} \right) = \frac{7}{7} + \frac{6}{5} = 1 + 1 \frac{1}{5} = 2 \frac{1}{5} \]
• \[ \frac{6}{7} + \frac{3}{5} + \frac{4}{7} + \frac{2}{5} = \left( \frac{6}{7} + \frac{4}{7} \right) + \left( \frac{3}{5} + \frac{2}{5} \right) = \frac{10}{7} + \frac{5}{5} = 1 \frac{3}{7} + 1 = 2 \frac{3}{7} \]
• \[ \frac{1}{3} + \frac{5}{6} + \frac{2}{3} = \left( \frac{1}{3} + \frac{2}{3} \right) + \frac{5}{6} = \frac{3}{3} + \frac{5}{6} = 1 + \frac{5}{6} = 1 \frac{5}{6} \]
• \[ \frac{3}{10} + \frac{8}{15} + \frac{2}{15} + \frac{7}{10} = \left( \frac{3}{10} + \frac{7}{10} \right) + \left( \frac{8}{15} + \frac{2}{15} \right) = \frac{10}{10} + \frac{10}{15} = 1 + \frac{2}{3} = 1 \frac{2}{3} \]
• \[ \frac{11}{24} + \frac{13}{24} = \frac{24}{24} = 1 \]
• \[ \frac{3}{5} + \frac{4}{7} + 6 \frac{2}{5} + \frac{1}{7} = \left( \frac{3}{5} + 6 \frac{2}{5} \right) + \left( \frac{4}{7} + \frac{1}{7} \right) = 6 \frac{5}{5} + \frac{5}{7} = 7 + \frac{5}{7} = 7 \frac{5}{7} \]
• \[ 1 + \frac{7}{12} + \frac{4}{9} = 1 \frac{7}{12} + \frac{4}{9} \]
• \[ 4 \frac{3}{8} + \frac{1}{12} + 3 \frac{5}{12} = 4 \frac{3}{8} + \left( \frac{1}{12} + 3 \frac{5}{12} \right) = 4 \frac{3}{8} + 3 \frac{6}{12} = 4 \frac{3}{8} + 3 \frac{1}{2} \]