4) \frac{(2,8+2\frac{2}{3}) \times 2,5}{10\frac{13}{30}-3,6};

4) Выполним вычисления:

$$2,8 + 2\frac{2}{3} = 2\frac{8}{10} + 2\frac{2}{3} = 2\frac{4}{5} + 2\frac{2}{3} = 4 + \frac{4}{5} + \frac{2}{3} = 4 + \frac{4 \cdot 3 + 2 \cdot 5}{15} = 4 + \frac{12+10}{15} = 4 + \frac{22}{15} = 4 + 1\frac{7}{15} = 5\frac{7}{15}$$.

$$5\frac{7}{15} \times 2,5 = \frac{5 \cdot 15 + 7}{15} \times \frac{25}{10} = \frac{75+7}{15} \times \frac{5}{2} = \frac{82 \times 5}{15 \times 2} = \frac{41 \times 5}{3 \times 2} = \frac{205}{6} = 34\frac{1}{6}$$.

$$10\frac{13}{30}-3,6 = 10\frac{13}{30} - 3\frac{6}{10} = 10\frac{13}{30} - 3\frac{18}{30} = 9\frac{43}{30} - 3\frac{18}{30} = 6\frac{25}{30} = 6\frac{5}{6}$$.

$$\frac{34\frac{1}{6}}{6\frac{5}{6}} = 34\frac{1}{6} : 6\frac{5}{6} = \frac{34 \cdot 6 + 1}{6} : \frac{6 \cdot 6 + 5}{6} = \frac{204+1}{6} : \frac{36+5}{6} = \frac{205}{6} : \frac{41}{6} = \frac{205}{6} \cdot \frac{6}{41} = \frac{205}{41} = 5$$.

Ответ: 5