Tính : a.1/5+4/11+4/5+7/11,b. 5/6+(5/9-1/4)

* Hướng dẫn giải

$a)\frac{1}{5} + \frac{4}{11}+ \frac{4}{5}+\frac{7}{11} = ( \frac{1}{5}+\frac{4}{5} ) + ( \frac{4}{11} +\frac{7}{11} ) = 1 + 1 = 2$

$b) \frac{5}{6} + ( \frac{5}{9}-\frac{1}{4} ) = \frac{1}{5} \frac{5}{6}+ ( \frac{20}{36} -\frac{9}{36} ) = \frac{5}{6} + \frac{11}{36} =\frac{30}{36} +\frac{11}{36} =\frac{41}{36}$