5. Which of the following statements are incorrect: $3.4 \in [2 ; 3.4) ; 3.4 \in [2 ; 3.4] ; 3.4 \in [2,3] ; 3.4 \in (2,5) ; 3.4 \in [3.4 ; 5)$ ?
Solution. The records $3.4 \in [2 ; 3.4)$ and $3.4 \in [2,3]$ are incorrect, since the number 3.4 does not satisfy the inequalities $2 \leqslant 3.4 < 3.4$ and $2 \leqslant 3.4 \leqslant 3$.