Hello,
I)
[tex] \dfrac{2}{5}=\dfrac{2*9*7}{5*9*7}=\dfrac{126}{315}[/tex]
[tex] \dfrac{4}{9}=\dfrac{4*5*7}{315}=\dfrac{140}{315}[/tex]
[tex] \dfrac{3}{7}=\dfrac{3*5*9}{315}=\dfrac{135}{315}[/tex]
or
[tex] \dfrac{126}{315}\leq\dfrac{135}{315}\leq\dfrac{140}{315}[/tex]
thus
[tex] \dfrac{2}{5}\leq\dfrac{3}{7}\leq\dfrac{4}{9}[/tex]
II)
[tex]\dfrac{\dfrac{1}{2}+\dfrac{5}{6}}{2}=\dfrac{8}{6*2}=\dfrac{2}{3}[/tex]
