Đáp án:
$a) \dfrac{-3}{4} + \dfrac{3}{7} + \dfrac{-1}{4} + \dfrac{4}{9} + \dfrac{4}{7}#
$= (-\dfrac{3}{4} +\dfrac{-1}{4}) +(\dfrac{3}{7} + \dfrac{4}{7}) + \dfrac{-1}{4}$
$= -1 +1 +\dfrac{-1}{4}$
$=\dfrac{-1}{4}$
$c) 8\dfrac{2}{7} - (3\dfrac{4}{9}+4\dfrac{2}{7})$
$=8\dfrac{2}{7} - 3\dfrac{4}{9} -4\dfrac{2}{7}$
$=\dfrac{58}{7} -\dfrac{31}{9} -\dfrac{30}{7}$
$=(\dfrac{58}{7} - \dfrac{30}{7}) -\dfrac{31}{9}$
$=\dfrac{28}{7} - \dfrac{31}{9}$
$=\dfrac{252}{63}- \dfrac{217}{63}$
$=\dfrac{35}{63}$
$=\dfrac{5}{9}$
