$\begin{array}{l} A = \left\{ {x|x + \dfrac{1}{3} \in Z\,\text{và}\,3 < x < 8} \right\}\\ + 3 < x < 8 \Rightarrow \dfrac{{10}}{3} < x + \dfrac{1}{3} < \dfrac{{25}}{3}\\ \Rightarrow x + \dfrac{1}{3} \in \left\{ {4;5;6;7;8} \right\}\\ \Rightarrow x \in \left\{ {\dfrac{{11}}{3};\dfrac{{14}}{3};\dfrac{{17}}{3};\dfrac{{20}}{3};\dfrac{{23}}{3}} \right\}\\ \Rightarrow A = \left\{ {\dfrac{{11}}{3};\dfrac{{14}}{3};\dfrac{{17}}{3};\dfrac{{20}}{3};\dfrac{{23}}{3}} \right\} \end{array}$
