Tính bằng cách thuận tiện.

\(\frac{5}{9}\,\, + \,\,\frac{5}{9}\,\, \times \,\,\frac{4}{5}\,\, + \,\,\frac{5}{9}\,\, \times \,\,\frac{{14}}{5}\)

= \(\frac{5}{9}\,\, \times \,\,\left( {1\,\, + \,\,\frac{4}{5}\,\, + \,\,\frac{{14}}{5}} \right)\)

= \(\frac{5}{9}\,\, \times \,\,\left( {\frac{5}{5}\,\, + \,\,\frac{4}{5}\,\, + \,\,\frac{{14}}{5}} \right)\)

= \(\frac{5}{9}\,\, \times \,\,\frac{{23}}{5}\) = \(\frac{{23}}{9}\)

\(\frac{{5\,\, \times \,\,7\,\, \times \,\,9}}{{2\,\, \times \,\,3\,\, \times \,\,7}}\)

= \(\frac{{5\,\, \times \,\,7\,\, \times \,\,3\,\, \times \,\,3}}{{2\,\, \times \,\,3\,\, \times \,\,7}}\)

= \(\frac{{5\,\, \times \,\,\cancel{7}\,\, \times \,\,\cancel{3}\,\, \times \,\,3}}{{2\,\, \times \,\,\cancel{3}\,\, \times \,\,\cancel{7}}}\)

= \(\frac{{5\,\, \times \,\,3}}{2}\) = \(\frac{{15}}{2}\)