Tính bằng cách thuận tiện (1 điểm) 5/2 × 3/5 + 5/2 × 1/5 + 5/2

\(\frac{5}{2}\,\, \times \,\,\frac{3}{5}\,\, + \,\,\frac{5}{2}\,\, \times \,\,\frac{1}{5}\,\, + \,\,\frac{5}{2}\)

\( = \frac{5}{2}\,\, \times \,\,\left( {\frac{3}{5}\,\, + \,\,\frac{1}{5}\,\, + \,1} \right)\)

\( = \frac{5}{2}\,\, \times \,\,\left( {\frac{3}{5}\,\, + \,\,\frac{1}{5}\,\, + \,\frac{5}{5}} \right)\)

\( = \frac{5}{2}\,\, \times \,\frac{9}{5}\)

\( = \frac{{\not 5}}{2}\,\, \times \,\frac{9}{{\not 5}}\)

\( = \frac{9}{2}\,\)