Tính 7/9 +3/8

\[\frac{7}{9}\,\, + \,\,\frac{3}{8}\,\, = \,\,\frac{{56}}{{72}}\,\, + \,\,\frac{{27}}{{72}}\,\, = \,\,\frac{{83}}{{72}}\]                            \(\frac{{12}}{5}\,\, + \,\,\frac{3}{{13}}\,\, = \,\,\frac{{156}}{{65}}\,\, + \,\,\frac{{15}}{{65}}\,\, = \,\,\frac{{171}}{{65}}\)

\(\frac{{13}}{7}\,\,:\,\,\frac{9}{8}\,\, = \,\,\frac{{13}}{7}\,\, \times \,\,\frac{8}{9}\,\, = \,\,\frac{{104}}{{63}}\)                                \(\frac{7}{{11}}\,\, - \,\,\frac{3}{7}\,\, = \,\,\frac{{49}}{{77}}\,\, - \,\,\frac{{33}}{{77}}\,\, = \,\,\frac{{16}}{{77}}\)