[tex]a=\frac{1}{2}+\frac{2}{3}+\frac{3}{4}+...+\frac{2012}{2013}\\
\\
b=\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+....+\frac{1}{2013}\\
\\
m_a=\frac{a+b}{2}\\
\\
m_a=\frac{\frac{1}{2}+\frac{2}{3}+..+\frac{2012}{2013}+\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2013}}{2} \\
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m_a=\frac{(\frac{1}{2}+\frac{1}{2})+(\frac{1}{3}+\frac{2}{3})+...+(\frac{1}{2013}+\frac{2012}{2013})}{2}\\
m_a=\frac{1+1+1+...+1(de\ 2012\ ori)}{2}\\
m_a=\frac{2012}{2}\Rightarrow \boxed{\boxed{\boxed{m_a=1006}}}[/tex]