a)
\(\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{101.102}\)
\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+....+\frac{1}{101}-\frac{1}{102}\)
\(=\frac{1}{2}-\frac{1}{102}=\frac{25}{51}\)
b)
\(\frac{5}{5.10}+\frac{5}{10.15}+....+\frac{5}{115.120}\)
\(=\frac{1}{5}-\frac{1}{120}=\frac{23}{120}\)
c)
\(\frac{2}{5.7}+\frac{2}{7.9}+.....+\frac{2}{997.99}\)
\(=\frac{1}{5}-\frac{1}{999}=\frac{994}{4995}\)
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