II. Phần tự luận. (7 điểm)

Điền dấu thích hợp vào ô trống. (1 điểm)

$\frac{4}{5}+\frac{9}{7}$ ..........$\frac{8}{7}-\frac{1}{10}$	$\frac{9}{4}\times 8$......... $\frac{5}{8}:\frac{5}{4}$
$\frac{23}{28}-\frac{4}{7}$ ......2	3 ....... $\frac{7}{9}+\frac{5}{7}$

\(\frac{4}{5}\,\, + \,\,\frac{9}{7}\,\, > \frac{8}{7}\,\, - \,\,\frac{1}{{10}}\)

Giải thích

\(\frac{4}{5}\,\, + \,\,\frac{9}{7}\, = \frac{{28}}{{35}} + \frac{{45}}{{35}} = \frac{{73}}{{35}}\)

\(\frac{8}{7}\,\, - \,\,\frac{1}{{10}} = \frac{{80}}{{70}} - \frac{7}{{70}} = \frac{{73}}{{70}}\)

So sánh: \(\frac{{73}}{{35}} > \frac{{73}}{{70}}\)

\(\frac{9}{4}\,\, \times \,\,8\,\, > \,\,\frac{5}{8}\,\,:\,\,\frac{5}{4}\)

Giải thích

\(\frac{9}{4} \times 8 = \frac{{9 \times 8}}{4} = \frac{{36}}{2}\)

\(\frac{5}{8}:\frac{5}{4} = \frac{5}{8} \times \frac{4}{5} = \frac{{\not 5}}{{\not 4 \times 2}} \times \frac{{\not 4}}{{\not 5}} = \frac{1}{2}\)

So sánh: \(\frac{{36}}{2} > \frac{1}{2}\)

\(\frac{{23}}{{28}}\,\, - \,\,\frac{4}{7}\,\, < \,2\)

Giải thích

\(\frac{{23}}{{28}}\,\, - \,\,\frac{4}{7}\, = \frac{{23}}{{28}} - \frac{{16}}{{28}} = \frac{7}{{28}}\)

So sánh: \(\frac{7}{{28}}\) < 1 < 2

\(\,3\,\, > \,\frac{7}{9}\,\, + \,\,\frac{5}{7}\,\)

Giải thích

\(\,3\,\, = \,\frac{3}{1}\,\, = \,\,\frac{{3 \times 63}}{{1 \times 63}}\, = \frac{{189}}{{63}}\)

\(\frac{7}{9}\,\, + \,\,\frac{5}{7}\, = \frac{{49}}{{63}} + \frac{{45}}{{63}} = \frac{{94}}{{63}}\)

So sánh:\(\frac{{189}}{{63}}\, > \frac{{94}}{{63}}\)