4)2 +5-4=

4) $$\begin{array}{rcl}2\frac{6}{7}+5\frac{5}{7}-4\frac{4}{7}&=&7\frac{11}{7}-4\frac{4}{7}=8\frac{4}{7}-4\frac{4}{7}=4\end{array}$$

Ответ: 4