[tex]M_a= \frac{a+b}{2} \\ a= \frac{1}{5} + \frac{1}{21} = \frac{26}{105} ; \\\\ b= \frac{9}{5} + \frac{41}{21} = \frac{574}{105} \\\\ \Rightarrow M_a= \frac{ \frac{26}{105}+ \frac{574}{105} }{2} = \frac{ \frac{600}{105} }{2} = \frac{ \frac{120}{21} }{2} = \frac{ \frac{40}{7} }{2} =\boxed{2,(857142).}[/tex]
