A = $\frac{1}{1.2}$ + $\frac{1}{2.3}$ + $\frac{1}{3.4}$ +... + $\frac{1}{2020.2021}$
A = $\frac{2 - 1}{1.2}$ + $\frac{3 - 2}{2.3}$ + $\frac{4 - 3}{3.4}$ +... + $\frac{2021 - 2020}{2020.2021}$
A = $\frac{2}{1.2}$ - $\frac{1}{1.2}$ + $\frac{3}{2.3}$ - $\frac{2}{2.3}$ +... + $\frac{2021}{2020.2021}$ - $\frac{2020}{2020.2021}$
A = 1 - $\frac{1}{2}$ + $\frac{1}{2}$ - $\frac{1}{3}$ +... + $\frac{1}{2020}$ - $\frac{1}{2021}$
A = 1 - $\frac{1}{2021}$
A = $\frac{2020}{2021}$
