Решение:

№1

1)

$$2 \cdot \frac{7}{10} = \frac{2 \cdot 7}{10} = \frac{14}{10} = \frac{7}{5} = 1\frac{2}{5} = 1,4$$

2)

$$7 \cdot \frac{5}{21} \cdot 6 = \frac{7 \cdot 5 \cdot 6}{21} = \frac{7 \cdot 5 \cdot 6}{7 \cdot 3} = \frac{5 \cdot 6}{3} = \frac{5 \cdot 3 \cdot 2}{3} = 5 \cdot 2 = 10$$

3)

$$\frac{42}{65} \cdot 13 \cdot \frac{5}{6} \cdot 7 = \frac{42 \cdot 13 \cdot 5 \cdot 7}{65 \cdot 6} = \frac{6 \cdot 7 \cdot 13 \cdot 5 \cdot 7}{13 \cdot 5 \cdot 6} = 7 \cdot 7 = 49$$

4)

$$45 \cdot \frac{1}{10} \cdot \frac{5}{18} \cdot 4 = \frac{45 \cdot 1 \cdot 5 \cdot 4}{10 \cdot 18} = \frac{9 \cdot 5 \cdot 5 \cdot 4}{5 \cdot 2 \cdot 9 \cdot 2} = \frac{5 \cdot 4}{2 \cdot 2} = \frac{5 \cdot 4}{4} = 5$$

№2

1)

$$12 \cdot (\frac{1}{3} - \frac{1}{4}) = 12 \cdot (\frac{4}{12} - \frac{3}{12}) = 12 \cdot \frac{1}{12} = \frac{12}{12} = 1$$

2)

$$15 \cdot (\frac{3}{5} + \frac{2}{3}) = 15 \cdot (\frac{9}{15} + \frac{10}{15}) = 15 \cdot \frac{19}{15} = \frac{15 \cdot 19}{15} = 19$$

3)

$$(\frac{13}{30} - \frac{11}{90}) \cdot 45 = (\frac{13 \cdot 3}{30 \cdot 3} - \frac{11}{90}) \cdot 45 = (\frac{39}{90} - \frac{11}{90}) \cdot 45 = \frac{28}{90} \cdot 45 = \frac{28 \cdot 45}{90} = \frac{28 \cdot 45}{45 \cdot 2} = \frac{28}{2} = 14$$

4)

$$(\frac{8}{21} - \frac{3}{14}) \cdot 42 = (\frac{8 \cdot 2}{21 \cdot 2} - \frac{3 \cdot 3}{14 \cdot 3}) \cdot 42 = (\frac{16}{42} - \frac{9}{42}) \cdot 42 = \frac{7}{42} \cdot 42 = \frac{7 \cdot 42}{42} = 7$$