(7/10-2/5)•(3/4+5/6):6 1/2

$( \frac{7}{10} - \frac{2}{5} ) \times ( \frac{3}{4} + \frac{5}{6}) \div 6 \frac{1}{2}$

решаем по действиям :

$1) \frac{7}{10} - \frac{2}{5} = \frac{7 \times 1}{10 \times 1} - \frac{2 \times 2}{5 \times 2} = \frac{7}{10} - \frac{4}{10} =$

$= \frac{7 - 4}{10} = \frac{3}{10}.$

$2) \frac{3}{4} + \frac{5}{6} = \frac{3 \times 3}{4 \times 3} + \frac{5 \times 2}{6 \times 2} = \frac{9}{12} + \frac{10}{12} =$

$= \frac{9 + 10}{12} = \frac{19}{12} = \frac{1 \times 12 + 7}{12} = 1 \frac{7}{12}.$

$3)1 \frac{7}{12} \div 6\frac{1}{2} = \frac{7 + 1 \times 12}{12} \div \frac{1 + 6 \times 12}{12} =$

$= \frac{19}{12} \div \frac{13}{2} = \frac{19}{12} \times \frac{2}{13} = \frac{38}{156 } = \frac{19}{78} .$

$4) \frac{3}{10} \times \frac{19}{78} = \frac{3 \times 19}{10 \times 78} = \frac{57}{180} = \frac{19}{260} .$

Ответ :

$\frac{19}{260} .$