Viết phân số thích hợp vào ô trống.

Giải thích:

\(\frac{4}{7}\,\, + \,\,\frac{3}{4}\,\, = \,\,\frac{{16}}{{28}}\,\, + \,\,\frac{{21}}{{28}}\,\, = \,\,\frac{{37}}{{28}}\)

\(\frac{{37}}{{28}}\,\, - \,\,\frac{9}{{14}}\,\, = \,\,\frac{{37}}{{28}}\,\, - \,\,\frac{{18}}{{28}}\,\, = \,\,\frac{{19}}{{28}}\)

\(\frac{{19}}{{28}}\,\, - \,\,\frac{1}{4}\,\, = \,\,\frac{{19}}{{28}}\,\, - \,\,\frac{7}{{28}}\,\, = \,\,\frac{{12}}{{28}}\,\, = \,\,\frac{3}{7}\)

\(\frac{3}{7}\,\, + \,\,\frac{1}{5}\,\, = \,\,\frac{{15}}{{35}}\,\, + \,\,\frac{7}{{35}}\,\, = \,\,\frac{{22}}{{35}}\)