[tex]\it \dfrac{4}{15}<\dfrac{4}{n}<\dfrac{1}{3} \Rightarrow \dfrac{^{4)}1}{\ 3}>\dfrac{4}{n}>\dfrac{4}{15} \Rightarrow \dfrac{4}{12}>\dfrac{4}{n}>\dfrac{4}{15} \Rightarrow \dfrac{12}{4}<\dfrac{n}{4}<\dfrac{15}{4} \Rightarrow \\ \\ \\ \Rightarrow 12<n<15 \Rightarrow n\in\{13,\ 14\}[/tex]
