Вычислите: а) (4/9 + 5/12) * 18/31 б) 6/25 * (11/15 - 9/20) в) (4 - 3 7/15) * 5/8 г) (1 1/24 - 5/12) * 4 1/8

а) $(\frac{4}{9} + \frac{5}{12}) \cdot \frac{18}{31} = (\frac{16}{36} + \frac{15}{36}) \cdot \frac{18}{31} = \frac{31}{36} \cdot \frac{18}{31} = \frac{31 \cdot 18}{36 \cdot 31} = \frac{18}{36} = \frac{1}{2} = 0,5$ б) $\frac{6}{25} \cdot (\frac{11}{15} - \frac{9}{20}) = \frac{6}{25} \cdot (\frac{44}{60} - \frac{27}{60}) = \frac{6}{25} \cdot \frac{17}{60} = \frac{6 \cdot 17}{25 \cdot 60} = \frac{1 \cdot 17}{25 \cdot 10} = \frac{17}{250} = 0,068$ в) $(4 - 3\frac{7}{15}) \cdot \frac{5}{8} = (3\frac{15}{15} - 3\frac{7}{15}) \cdot \frac{5}{8} = \frac{8}{15} \cdot \frac{5}{8} = \frac{8 \cdot 5}{15 \cdot 8} = \frac{5}{15} = \frac{1}{3}$ г) $(1\frac{1}{24} - \frac{5}{12}) \cdot 4\frac{1}{8} = (1\frac{1}{24} - \frac{10}{24}) \cdot \frac{33}{8} = (\frac{25}{24} - \frac{10}{24}) \cdot \frac{33}{8} = \frac{15}{24} \cdot \frac{33}{8} = \frac{5}{8} \cdot \frac{33}{8} = \frac{165}{64} = 2\frac{37}{64}$