2:
b) Có: B = $\frac{1}{1.102} + \frac{1}{2.103} + \frac{1}{3.104} + ... + \frac{1}{299.400}$
101B=\frac{101}{1.102}+\frac{101}{2.103}+\frac{101}{3.104}+...+\frac{101}{299.400}
B=\frac{1}{101}(\frac{101}{1.102}+\frac{101}{2.103}+\frac{101}{3.104}+...+\frac{101}{299.400})...