Tính bằng cách thuận tiện.

\(\frac{4}{5}\,\, \times \,\,\frac{3}{7}\,\, + \,\,\frac{4}{5}\,\, \times \,\,\frac{6}{7}\,\, - \,\,\frac{4}{5}\,\, \times \,\,\frac{4}{{14}}\)

= \(\frac{4}{5}\,\, \times \,\,\left( {\frac{3}{7}\,\, + \,\,\frac{6}{7}\,\, - \,\,\frac{4}{{14}}} \right)\)

= \(\frac{4}{5}\,\, \times \,\,\left( {\frac{3}{7}\,\, + \,\,\frac{6}{7}\,\, - \,\,\frac{2}{7}} \right)\)

= \(\frac{4}{5}\,\, \times \,\,\frac{7}{7}\)

= \(\frac{4}{5}\,\, \times \,\,1\) = \(\frac{4}{5}\)