$\dfrac{4}{9}+$ $\dfrac{5}{7}=$ $\dfrac{28}{63}+$ $\dfrac{45}{63}=$ $\dfrac{73}{63}$
$\dfrac{4}{9}-$ $\dfrac{5}{7}=$ $\dfrac{28}{63}-$ $\dfrac{45}{63}=$ $-\dfrac{17}{63}$
$\dfrac{7}{4}-$ $\dfrac{5}{12}=$ $\dfrac{21}{12}-$ $\dfrac{5}{12}=$ $\dfrac{16}{12}=$ $\dfrac{4}{3}$
$\dfrac{5}{6}$ x $\dfrac{9}{10}=$ $\dfrac{45}{60}=$ $\dfrac{3}{4}$
$\dfrac{7}{12}:$ $\dfrac{3}{8}=$ $\dfrac{7}{12}$ x $\dfrac{8}{3}=$ $\dfrac{56}{36}=$ $\dfrac{14}{9}$
~Xin hay nhất~
