5.471 Выполните действия: a) (\frac{4}{9} + \frac{2}{9}) \cdot \frac{9}{13}; в) (\frac{9}{11} - \frac{4}{11}).

Решение:

a) \((\frac{4}{9} + \frac{2}{9}) \cdot \frac{9}{13} = \frac{4+2}{9} \cdot \frac{9}{13} = \frac{6}{9} \cdot \frac{9}{13} = \frac{6 \cdot 9}{9 \cdot 13} = \frac{6 \cdot \cancel{9}}{\cancel{9} \cdot 13} = \frac{6}{13}\)

в) \(\frac{9}{11} - \frac{4}{11} = \frac{9-4}{11} = \frac{5}{11}\)