11) 3 1/2 : (1 4/15 + 2 9/10)

11) \(3\frac{1}{2} : (1\frac{4}{15} + 2\frac{9}{10}) = \frac{7}{2} : (\frac{19}{15} + \frac{29}{10}) = \frac{7}{2} : (\frac{38}{30} + \frac{87}{30}) = \frac{7}{2} : \frac{125}{30} = \frac{7}{2} \cdot \frac{30}{125} = \frac{7}{1} \cdot \frac{15}{125} = \frac{7 \cdot 3}{25} = \frac{21}{25}\)
Ответ: 21/25