\(A=\frac{1+\frac{1}{3}+\frac{1}{5}+...+\frac{1}{97}+\frac{1}{99}}{\frac{1}{1\cdot99}+\frac{1}{3\cdot97}+...+\frac{1}{97\cdot3}+\frac{1}{99\cdot1}}=\frac{\left[1+\frac{1}{99}\right]+\left[\frac{1}{3}+\frac{1}{97}\right]+...+\left[\frac{1}{49}+\frac{1}{51}\right]}{2\left[\frac{1}{1\cdot99}+\frac{1}{3\cdot97}+...+\frac{1}{49\cdot51}\right]}\)
\(=\frac{\frac{100}{1\cdot99}+\frac{100}{3\cdot97}+...+\frac{100}{49.51}}{2\left[\frac{1}{1\cdot99}+\frac{1}{3\cdot97}+...+\frac{1}{49.51}\right]}=\frac{100\left[\frac{1}{1\cdot99}+\frac{1}{3\cdot97}+...+\frac{1}{49.51}\right]}{2\left[\frac{1}{1\cdot99}+\frac{1}{3\cdot97}+...+\frac{1}{49.51}\right]}=\frac{100}{2}=50\)
