[tex]\it \dfrac{a}{b}=\dfrac{2}{7} \Rightarrow \dfrac{b}{a}=\dfrac{7}{2} \Rightarrow \dfrac{b}{a}=3,5 \Rightarrow b=3,5a\ \ \ \ \ \ (*)\\ \\ \\ \dfrac{2a+b}{5a+2b}\ \stackrel{(*)}{=}\ \dfrac{2a+3,5a}{5a+7a}=\dfrac{5,5a}{7a}=\dfrac{^{2)}5,5}{\ \ 7}=\dfrac{11}{14}[/tex]
