Lời giải:
\(\frac{2000}{2001}=1-\frac{1}{2001}\)
\(\frac{2001}{2002}=1-\frac{1}{2002}\)
Vì $\frac{1}{2001}> \frac{1}{2002}$ nên $1-\frac{1}{2001}< 1-\frac{1}{2002}$
Hay $\frac{2000}{2001}< \frac{2001}{2002}$
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$\frac{13}{25}> \frac{13}{26}=\frac{1}{2}=\frac{7}{14}> \frac{7}{15}$
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$\frac{23}{45}> \frac{23}{46}=\frac{1}{2}=\frac{19}{38}> \frac{19}{39}$

4 và 5