So sánh các phân số sau:

* Hướng dẫn giải

a) $\frac{219}{220}+\frac{1}{220}=\frac{215}{216}+\frac{1}{216}=1$

$Mà \frac{1}{220}<\frac{1}{216} nên \frac{219}{220}>\frac{215}{216}$

$\begin{array}{l}b)Tacó:\frac{-1999}{2000}+\frac{-1}{2001}=\frac{-2000}{2001}+\frac{-1}{2001}=-1\\ \\ Mà \frac{1}{220}<\frac{1}{216} nên \frac{219}{220}>\frac{215}{216}\end{array}$

$\begin{array}{l}c)Tacó:\frac{403}{407}+\frac{4}{407}=\frac{813}{817}+\frac{4}{817}=1\\ \\ Mà \frac{4}{407}<\frac{4}{817} nên \frac{403}{407}<\frac{813}{817}\end{array}$

$\begin{array}{l}d)Tacó:\frac{-251}{138}+\frac{-25}{138}=\frac{-317}{171}+\frac{-25}{172}=-2\\ \\ Mà \frac{-25}{138}<\frac{15}{138} nên \frac{-251}{138}>\frac{-317}{171}\end{array}$