a, $\dfrac{25}{13}$ và $\dfrac{257}{137}$
Ta có: $\dfrac{25}{13}=1+\dfrac{12}{13}=1+\dfrac{120}{130}$
$\dfrac{257}{137}=1+\dfrac{120}{137}$
Vì $137>120⇒\dfrac{120}{130}>\dfrac{120}{137}$
$⇒\dfrac{25}{13}>\dfrac{257}{137}$
b, $\dfrac{22}{175}$ và $\dfrac{47}{349}$
Ta có: $\dfrac{22}{175}=\dfrac{44}{350}$
Vì $44<47$
$350>349$
$⇒\dfrac{44}{350}<\dfrac{47}{349}$
$⇒\dfrac{22}{175}<\dfrac{47}{349}$