Diện tích hình thang có độ dài đáy a, b và chiều cao c là: (0,5 điểm)  

a) \(\frac{{15}}{9} - \frac{1}{2}\,\,\)<  \(\frac{3}{2} + \frac{2}{9}\)

Giải thích:

\(\frac{{15}}{9} - \frac{1}{2}\,\, = \,\,\frac{{30}}{{18}}\,\, - \,\frac{9}{{18}}\,\, = \,\,\frac{7}{6} = \frac{{21}}{{18}}\)

\(\frac{3}{2} + \frac{2}{9}\) =  \(\frac{{27}}{{18}} + \,\frac{4}{{18}}\,\,\)=\(\frac{{31}}{{18}}\)

\(\frac{{21}}{{18}}\,\, < \,\,\frac{{31}}{{18}}\)

Vậy: \(\frac{{15}}{9} - \frac{1}{2}\,\,\, < \,\,\frac{3}{2} + \frac{2}{9}\)

c) \(\frac{1}{5} \times \frac{5}{4}\,\, < \,\,\frac{1}{2}:\frac{3}{2}\) 

Giải thích:

\(\frac{1}{5} \times \frac{5}{4}\,\,\, = \,\,\frac{1}{4}\, = \frac{3}{{12}}\)

\(\frac{1}{2}:\frac{3}{2}\,\, = \,\,\frac{1}{3} = \frac{4}{{12}}\)

\(\frac{4}{{12}}\,\,\, > \,\,\,\frac{3}{{12}}\)

Vậy: \(\frac{1}{5} \times \frac{5}{4}\,\, < \,\,\frac{1}{2}:\frac{3}{2}\)