\(\frac{B}{A}=\frac{\frac{1}{99}+\frac{2}{98}+\frac{3}{97}+...+\frac{99}{1}}{\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{100}}\)
\(\frac{B}{A}=\frac{1+\left[\frac{1}{99}+1\right]+\left[\frac{2}{98}+1\right]+\left[\frac{3}{97}+1\right]+...+\left[\frac{98}{2}+1\right]}{\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{100}}\)
\(\frac{B}{A}=\frac{\frac{100}{100}+\frac{100}{99}+\frac{100}{98}+\frac{100}{97}+...+\frac{100}{2}}{\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{100}}\)
\(\frac{B}{A}=\frac{100\cdot\left[\frac{1}{100}+\frac{1}{99}+\frac{1}{98}+...+\frac{1}{2}\right]}{\left[\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{100}\right]}=100\)
Vậy : \(\frac{B}{A}=100\)
Ta có:
\(B=\frac{1}{99}+\frac{2}{98}+...+\frac{99}{1}\)
\(=\left(1+\frac{1}{99}\right)+\left(1+\frac{2}{98}\right)+...+\left(1+\frac{98}{2}\right)+1\)
\(=\frac{100}{99}+\frac{100}{98}+...+\frac{100}{2}+\frac{100}{100}\)
\(=100\left(\frac{1}{2}+\frac{1}{3}+...+\frac{1}{99}+\frac{1}{100}\right)\)
\(=100.A\)
\(\Rightarrow\frac{B}{A}=100\)
