Tính nhanh: (1 điểm)

a) 2,5 × 1,2 + 2,5 × 2,1 + 2,5 × 0,7 =  =  =

b) 0,8 × 45 × 2 =  =  =

a) \(\frac{7}{3} + \frac{2}{9}\) >  \(\frac{1}{3} - \frac{1}{9}\)

b) \(\frac{2}{5} \times \frac{1}{6}\)   <  \(\frac{3}{2}:\frac{1}{{15}}\)

Giải thích:

\(\,\frac{7}{3}\,\, + \,\,\frac{2}{9} = \,\,\frac{{23}}{9}\)

\(\frac{1}{3} - \frac{1}{9}\,\, = \,\,\frac{2}{9}\,\,\)

\(\frac{{23}}{9}\,\, > \,\frac{2}{9}\)

Vậy: \(\frac{7}{3} + \frac{2}{9}\) >  \(\frac{1}{3} - \frac{1}{9}\)

Giải thích:

\(\frac{2}{5} \times \frac{1}{6}\,\,\, = \,\,\frac{2}{{30}}\)

\(\frac{3}{2}:\frac{1}{{15}}\,\, = \,\,\frac{3}{2}\,\, \times \,\,15\,\, = \,\,\frac{{45}}{2}\)

\(\frac{2}{{30}}\,\, < \,\,\,\frac{{45}}{2}\)

Vậy: \(\frac{2}{5} \times \frac{1}{6}\)   <  \(\frac{3}{2}:\frac{1}{{15}}\)