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

\(= \left(\right. \frac{- 5}{9} + \frac{- 4}{9} \left.\right) + \left(\right. \frac{8}{15} + \frac{7}{15} \left.\right) + \frac{- 2}{11}\)

\(= - 1 + 1 + \frac{- 2}{11}\)

\(= \frac{- 2}{11}\)

b) \(\left(\right. \frac{7}{2} \cdot \frac{5}{6} \left.\right) + \left(\right. \frac{7}{6} : \frac{2}{7} \left.\right)\)

\(= \frac{7}{6} \cdot \frac{5}{2} + \frac{7}{6} \cdot \frac{7}{2}\)

\(= \frac{7}{6} \cdot \left(\right. \frac{5}{2} + \frac{7}{2} \left.\right)\)

\(=\frac{7}{6}\cdot1_{}=\frac76\)

a)Ta có:

\(\frac{- 3}{8} = \frac{\left(\right. - 3 \left.\right) . 3}{8.3} = \frac{- 9}{24}\)

\(\frac{5}{- 12} = \frac{- 5}{12} = \frac{- 5.2}{12.2} = \frac{- 10}{24}\)

Vì \(\frac{- 9}{24} > \frac{- 10}{24}\) nên \(\frac{- 3}{8} > \frac{5}{- 12}\)

b)Ta có:

\(\frac{3131}{5252} = \frac{3131 : 101}{5252 : 101} = \frac{31}{52}\)

\(\frac{31}{52} = \frac{31}{52}\)

Vì \(\frac{31}{52} = \frac{31}{52}\) nên \(\frac{3131}{5252} = \frac{31}{52}\)

a)Ta có:

\(\frac{- 3}{8} = \frac{\left(\right. - 3 \left.\right) . 3}{8.3} = \frac{- 9}{24}\)

\(\frac{5}{- 12} = \frac{- 5}{12} = \frac{- 5.2}{12.2} = \frac{- 10}{24}\)

Vì \(\frac{- 9}{24} > \frac{- 10}{24}\) nên \(\frac{- 3}{8} > \frac{5}{- 12}\)

b)Ta có:

\(\frac{3131}{5252} = \frac{3131 : 101}{5252 : 101} = \frac{31}{52}\)

\(\frac{31}{52} = \frac{31}{52}\)

Vì \(\frac{31}{52} = \frac{31}{52}\) nên \(\frac{3131}{5252} = \frac{31}{52}\)