1.79 Вычислите: а) (7/30 + 1/2 + 4/15) : (49/50 − 14/25 − 2/5); б) 39 : (3/8 + 1/6) + (3/10)^2 · (2/3 − 7/18).

а) \[\frac7{30}+\frac12+\frac4{15}=\frac7{30}+\frac{15}{30}+\frac8{30}=1\]

\[\frac{49}{50}-\frac{14}{25}-\frac25=\frac{49}{50}-\frac{28}{50}-\frac{20}{50}=\frac1{50}\]

\[1:\frac1{50}=50\]

б) \[\frac38+\frac16=\frac9{24}+\frac4{24}=\frac{13}{24}\]

\[39:\frac{13}{24}=39\cdot\frac{24}{13}=72\]

\[\left(\frac3{10}\right)^2\left(\frac23-\frac7{18}\right)=\frac9{100}\left(\frac{12}{18}-\frac7{18}\right)=\frac9{100}\cdot\frac5{18}=\frac1{40}\]

\[72+\frac1{40}=72\frac1{40}\]

Ответ: а) \(50\); б) \(72\frac1{40}\).