$\frac{2}{1.3}$ + $\frac{2}{3.5}$ + $\frac{2}{5.7}$ + ... + $\frac{2}{99.101}$
= $\frac{1}{1}$ - $\frac{1}{3}$ + $\frac{1}{3}$ - $\frac{1}{5}$ + $\frac{1}{5}$ - $\frac{1}{7}$ + ... + $\frac{1}{99}$ - $\frac{1}{101}$
= 1 - $\frac{1}{101}$
= $\frac{100}{101}$
Chúc học tốt!!!