7) $\left(\frac{3}{4}-\frac{1}{6}\right)\cdot3$; 8) $\left(\frac{2}{5}+\frac{13}{15}\right)\cdot6$; 9) $\left(\frac{3}{8}-\frac{1}{20}\right)\cdot10$; 10) $\left(\frac{2}{20}+\frac{7}{30}\right)\cdot15$; 11) $\left(\frac{9}{10}-\frac{7}{15}\right)\cdot3$; 12) $\left(\frac{1}{6}+\frac{1}{4}\right)\cdot9$.

Question

Вопрос: $Фото задания: 7) $\left(\frac{3}{4}-\frac{1}{6}\right)\cdot3$; 8) $\left(\frac{2}{5}+\frac{13}{15}\right)\cdot6$; 9)…$ Фото задания

Accepted Answer

Приводим дроби к общему знаменателю, затем выполняем умножение:
$\left(\frac{3}{4}-\frac{1}{6}\right)\cdot3=\left(\frac{9}{12}-\frac{2}{12}\right)\cdot3=\frac{7}{12}\cdot3=\frac{7}{4}=1\frac{3}{4}$.
$\left(\frac{2}{5}+\frac{13}{15}\right)\cdot6=\left(\frac{6}{15}+\frac{13}{15}\right)\cdot6=\frac{19}{15}\cdot6=\frac{38}{5}=7\frac{3}{5}$.
$\left(\frac{3}{8}-\frac{1}{20}\right)\cdot10=\left(\frac{15}{40}-\frac{2}{40}\right)\cdot10=\frac{13}{40}\cdot10=\frac{13}{4}=3\frac{1}{4}$.
$\left(\frac{2}{20}+\frac{7}{30}\right)\cdot15=\left(\frac{3}{30}+\frac{7}{30}\right)\cdot15=\frac{1}{3}\cdot15=5$.
$\left(\frac{9}{10}-\frac{7}{15}\right)\cdot3=\left(\frac{27}{30}-\frac{14}{30}\right)\cdot3=\frac{13}{30}\cdot3=\frac{13}{10}=1\frac{3}{10}$.
$\left(\frac{1}{6}+\frac{1}{4}\right)\cdot9=\left(\frac{2}{12}+\frac{3}{12}\right)\cdot9=\frac{5}{12}\cdot9=\frac{15}{4}=3\frac{3}{4}$.

Ответ: 7) $1\frac{3}{4}$; 8) $7\frac{3}{5}$; 9) $3\frac{1}{4}$; 10) $5$; 11) $1\frac{3}{10}$; 12) $3\frac{3}{4}$.