a) \(\dfrac{-5}{9}\) + \(\dfrac{8}{15}\) + \(\dfrac{-2}{11}\) + \(\dfrac{4}{-9}\) + \(\dfrac{7}{15}\) = ( \(\dfrac{-5}{9}\) + \(\dfrac{-4}{9}\) ) + ( \(\dfrac{8}{15}\) + \(\dfrac{7}{15}\) ) + \(\dfrac{-2}{11}\)

= \(\dfrac{-9}{9}\) + \(\dfrac{15}{15}\) + \(\dfrac{-2}{11}\)

= -1 + 1 + \(\dfrac{-2}{11}\)

= 0 + \(\dfrac{-2}{11}\) = \(\dfrac{-2}{11}\)

b) ( \(\dfrac{7}{2}\)\(\div\dfrac{5}{6}\) ) + ( \(\dfrac{7}{6}\div\dfrac{7}{2}\) )

=\(\left(\dfrac{7}{2}\times\dfrac{5}{6}\right)+\left(\dfrac{7}{6}\times\dfrac{7}{2}\right)\)

=\(\dfrac{7}{2}\times\left(\dfrac{5}{6}+\dfrac{7}{6}\right)\)

= \(\dfrac{7}{2}\times2\)

= 7

a) có \(\dfrac{-3}{8}\) = \(\dfrac{-9}{24}\); \(\dfrac{-5}{12}\) =\(\dfrac{-10}{12}\)

vì \(\dfrac{-9}{24}\) > \(\dfrac{-10}{24}\) nên \(\dfrac{-3}{8}\) > \(\dfrac{5}{-12}\)

b) có \(\dfrac{3131}{5252}\) = \(\dfrac{3131\div101}{5252\div101}\) = \(\dfrac{31}{52}\)

vậy \(\dfrac{3131}{5252}\) = \(\dfrac{31}{52}\)