Tính bằng cách thuận tiện.

\[\frac{7}{{48}}\,\, \times \,\,\frac{8}{9}\,\, + \,\,\frac{7}{{48}}\,\, \times \,\,\frac{4}{9}\] = …………………………………….. = …………………………………….. = …………………………………….. = ……………………………………..

\[\frac{5}{9}\,\, + \,\,\left( {\frac{7}{8}\,\, + \,\,\frac{4}{9}} \right)\] = …………………………………….. = …………………………………….. = …………………………………….. = ……………………………………..

\[\frac{7}{{48}}\,\, \times \,\,\frac{8}{9}\,\, + \,\,\frac{7}{{48}}\,\, \times \,\,\frac{4}{9}\]

= \[\frac{7}{{48}}\,\, \times \,\,\left( {\frac{8}{9}\,\, + \,\,\frac{4}{9}} \right)\]

= \[\frac{7}{{48}}\,\, \times \,\,\frac{{12}}{9}\]

= \[\frac{{7\,\, \times \,\,12}}{{4\,\, \times \,\,12\,\, \times \,\,9}}\] = \[\frac{7}{{36}}\]

\[\frac{5}{9}\,\, + \,\,\left( {\frac{7}{8}\,\, + \,\,\frac{4}{9}} \right)\]

= \[\frac{5}{9}\,\, + \,\,\frac{4}{9}\,\, + \,\,\frac{7}{8}\]

= \[1\,\, + \,\,\frac{7}{8}\]

= \[\frac{8}{8}\,\, + \,\,\frac{7}{8}\]

= \[\frac{{15}}{8}\]