Вычислите: (2 1/4 + 3 2/3) : (8,5 − 1 2/5) − 1,2.

Преобразуем смешанные числа и десятичные дроби:

\(2\dfrac{1}{4}=\dfrac{9}{4}\), \(3\dfrac{2}{3}=\dfrac{11}{3}\), \(8.5=\dfrac{17}{2}\), \(1\dfrac{2}{5}=\dfrac{7}{5}\), \(1.2=\dfrac{6}{5}\).

\(\left(\dfrac{9}{4}+\dfrac{11}{3}\right):\left(\dfrac{17}{2}-\dfrac{7}{5}\right)-\dfrac{6}{5}\)

\(=\dfrac{71}{12}:\dfrac{71}{10}-\dfrac{6}{5}=\dfrac{71}{12}\cdot\dfrac{10}{71}-\dfrac{6}{5}\)

\(=\dfrac{5}{6}-\dfrac{6}{5}=\dfrac{25-36}{30}=-\dfrac{11}{30}\).

Ответ: \(-\dfrac{11}{30}\).