Tính tổng sau

 Tính tổng sau
 $$\begin{gathered} \mathrm{A}=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+....+\frac{1}{99.100} \\ \mathrm{B}=\frac{2}{1.3}+\frac{2}{5.7}+\frac{2}{7.9}+....+\frac{2}{48.50} \\ \mathrm{C}=\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+.....+\frac{1}{2003.2005} \end{gathered}$$