Найдите значение выражения: а)25*(7/10+3/5+1/2) б)30:(5/7+1/28+3/4)...

А)
$25(\frac{7}{10}+\frac{3}{5}+н)=25(0,7+0,6+0,5)=25*1,8=45;$
б)
$\frac{30}{\frac{5}{7}+\frac{1}{28}+\frac{3}{4}}=\frac{30}{\frac{20}{28}+\frac{1}{28}+\frac{21}{28}}=\frac{30}{\frac{42}{28}}=30*\frac{28}{42}=5*\frac{28}{7}=20;$
в)
$\frac{\frac{5}{12}+\frac{1}{6}+\frac{3}{8}}{\frac{15}{16}}=\frac{\frac{10}{24}+\frac{4}{24}+\frac{9}{24}}{\frac{15}{16}}=\frac{23}{24}:\frac{15}{16}=\frac{23}{24}*\frac{16}{15}=\frac{23}{3}*\frac{2}{15}=\frac{46}{45}=1\frac{1}{45};$
г)
$(\frac{3}{5}-\frac{4}{15})(\frac{1}{2}-\frac{1}{3})=(\frac{9}{15}-\frac{4}{15})(\frac{3}{6}-\frac{2}{6})=\frac{5}{15}*\frac{1}{6}=\frac{5}{90}=\frac{1}{18};$
д)
$\frac{\frac{2}{3}+\frac{5}{9}}{\frac{1}{9}+\frac{1}{3}}=\frac{\frac{6}{9}+\frac{5}{9}}{\frac{1}{9}+\frac{3}{9}}=\frac{11}{9}:\frac{4}{9}=\frac{11}{9}*\frac{9}{4}=\frac{11}{4}=2,75;$
е)
$(\frac{7}{8}+\frac{6}{7})(\frac{7}{8}-\frac{6}{7})=(\frac{49}{56}+\frac{48}{56})(\frac{49}{56}-\frac{48}{56})=\frac{97}{56}*\frac{1}{56}=\frac{97}{3136}.$