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Решите задачу:

$13) \frac{7}{18} \times \frac{9}{14} + \frac{1}{3} \times \frac{6}{7} = \frac{1}{4} + \frac{2}{7} = \frac{15}{28} .$

$14) \frac{9}{20} \times \frac{2}{3} + \frac{5}{14} \times \frac{7}{25} = \frac{3}{10} + \frac{1}{10} = \frac{2}{5} .$

$15)3 \frac{3}{4} \times \frac{2}{5} - 3 \frac{6}{25} \times \frac{5}{27} = 1 \frac{1}{2} - \frac{3}{5} = \frac{9}{10} .$

$16)2 \frac{2}{5} \times \frac{5}{6} - \frac{3}{4} \times 1 \frac{2}{3} = 2 - 1 \frac{1}{4} = \frac{3}{4} .$

$17)1 \frac{17}{28} \times \frac{14}{9} + \frac{14}{25} \times \frac{5}{7} = 2 \frac{1}{2} + \frac{2}{5} = 2 \frac{9}{10} .$

$18)5 \frac{1}{4} \times 8 + 3 \frac{1}{2} \times 8 = 42 + 28 = 70.$