II. Phần tự luận. (7 điểm)

Điền số thích hợp vào chỗ chấm. (2 điểm)

\(\frac{4}{5}\,\, + \,\,.........\,\, = \,\,\frac{{61}}{{45}}\)	\(...........\,\, - \,\,\frac{2}{7}\,\, = \,\,\frac{{31}}{{63}}\)
\(\frac{9}{{17}}\,\,:\,\,.........\,\, = \,\,2\)	\(\frac{8}{9}\,\, \times \,\,...........\,\, = \,\,\frac{1}{2}\)

\(\frac{4}{5}\,\, + \,\frac{{25}}{{45}} = \,\,\frac{{61}}{{45}}\)

Giải thích:

\(\frac{4}{5}\,\, + \,\,.........\,\, = \,\,\frac{{61}}{{45}}\)

\(\,.........\,\, = \,\,\frac{{61}}{{45}} - \frac{4}{5}\)

\(\,.........\,\, = \,\,\frac{{61}}{{45}} - \frac{{4 \times 9}}{{5 \times 9}}\)

\(\,.........\,\, = \,\,\frac{{61}}{{45}} - \frac{{36}}{{45}}\)

\(\,.........\,\, = \,\,\frac{{25}}{{45}}\)

\(\frac{{49}}{{63}}\, - \,\,\frac{2}{7}\,\, = \,\,\frac{{31}}{{63}}\)

Giải thích:

\(...........\,\, - \,\,\frac{2}{7}\,\, = \,\,\frac{{31}}{{63}}\)

\(...........\,\,\,\, = \,\,\frac{{31}}{{63}} + \frac{2}{7}\)

\(...........\,\,\,\, = \,\,\frac{{31}}{{63}} + \frac{{2 \times 9}}{{7 \times 9}}\)

\(...........\,\,\,\, = \,\,\frac{{31}}{{63}} + \frac{{18}}{{63}}\)

\(...........\,\,\,\, = \,\,\frac{{49}}{{63}}\)

\(\frac{9}{{17}}\,\,:\,\,\frac{9}{{34}}\, = \,\,2\)

Giải thích:

\(.........\, = \frac{9}{{17}}\,:\,2\)

\(.........\, = \frac{9}{{17}}\, \times \frac{1}{2}\)

\(.........\, = \frac{9}{{34}}\,\)

\(\frac{8}{9}\,\, \times \,\,\frac{9}{{16}}\,\, = \,\,\frac{1}{2}\)

Giải thích:

\(\frac{8}{9}\,\, \times \,\,...........\,\, = \,\,\frac{1}{2}\)

\(\,\,...........\,\, = \,\,\frac{1}{2}:\frac{8}{9}\)

\(\,\,...........\,\, = \,\,\frac{1}{2} \times \frac{9}{8}\)

\(\,\,...........\,\, = \,\,\frac{9}{{16}}\)