Điền dấu vào chỗ chấm.

Hướng dẫn giải

a)

\[\frac{5}{8} + \frac{1}{4} = \frac{5}{8} + \frac{2}{8} = \frac{{5 + 2}}{8} = \frac{7}{8}\]

\[1 - \frac{1}{8} = \frac{8}{8} - \frac{1}{8} = \frac{{8 - 1}}{8} = \frac{7}{8}\]

Vì \(\frac{7}{8} = \frac{7}{8}\)nên \[\frac{5}{8} + \frac{1}{4} = 1 - \frac{1}{8}\]

b)

\[\frac{1}{5} \times \frac{1}{4} = \frac{{1 \times 1}}{{5 \times 4}} = \frac{1}{{20}} = \frac{7}{{140}}\]

\[\frac{1}{7} \times 2 = \frac{1}{7} \times \frac{2}{1} = \frac{{1 \times 2}}{{7 \times 1}} = \frac{2}{7} = \frac{{40}}{{140}}\]

Vì \(\frac{7}{{140}} < \frac{{40}}{{140}}\)nên \[\frac{1}{5} \times \frac{1}{4} < \frac{1}{7} \times 2\]