So sánh hai phân số sau bằng cách nhanh nhất 2009 2007 và 1999 1997

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a)$\frac{2007}{2008}$ =1-$\frac{1}{2008}$ 

$\frac{2009}{2010}$ =1-$\frac{1}{2010}$

Mà $\frac{1}{2008}$ >$\frac{1}{2010}$

⇒1-$\frac{1}{2008}$ <1-$\frac{1}{2010}$

⇒$\frac{2007}{2008}$<$\frac{2009}{2010}$

b)$\frac{25}{68}$ <$\frac{1}{2}$

$\frac{20}{35}$> $\frac{1}{2}$ 

⇒$\frac{20}{35}$>$\frac{25}{68}$

c)$\frac{17}{68}$ =$\frac{1}{4}$ 

$\frac{1}{4}$ >$\frac{1}{5}$

⇒$\frac{17}{68}$>$\frac{1}{5}$