2. Вычислите: 6 3/4 : 3 + 27/40 · (6 7/12 − 3 17/36) · 2 1/2 − 4 1/3 : 13/20 − 1 1/4.

Преобразуем смешанные числа:

\(6\frac34=\frac{27}{4}\), \(6\frac7{12}=\frac{79}{12}\), \(3\frac{17}{36}=\frac{125}{36}\), \(2\frac12=\frac52\), \(4\frac13=\frac{13}{3}\), \(1\frac14=\frac54\).

\(\frac{27}{4}:3=\frac94\).

\(\frac{79}{12}-\frac{125}{36}=\frac{237-125}{36}=\frac{112}{36}=\frac{28}{9}\).

\(\frac{27}{40}\cdot\frac{28}{9}\cdot\frac52=\frac{49}{12}\).

\(\frac{13}{3}:\frac{13}{20}=\frac{20}{3}\).

Итак, \(\frac94+\frac{49}{12}-\frac{20}{3}-\frac54=\frac{27+49-80-15}{12}=-\frac{19}{12}\).

Ответ: \(-\frac{19}{12}=-1\frac7{12}\).