1)Cho A=\(\frac{196}{197}\)+\(\frac{197}{198}\)
B=\(\frac{196+197}{197+198}\)
So sánh A và B
2)Cho B=\(\frac{1}{4}\)+\(\frac{1}{5}+\frac{1}{6}+\frac{1}{7}+...+\frac{1}{19}\).Chứng minh B>1
3)Tính nhanh
\(\frac{\frac{3}{5}+\frac{3}{7}-\frac{3}{11}}{\frac{4}{5}+\frac{4}{7}-\frac{4}{11}}\)