Thực hiện phép tính (Tính hợp lí nếu có thể) 2/7:7/6-0,5

a) \(\frac{2}{7} \cdot \frac{7}{6} - 0,5\)

\( = \frac{2}{6} - \frac{1}{2}\)

\( = \frac{1}{3} - \frac{1}{2}\)

\( = \frac{2}{6} - \frac{3}{6}\)

\( = - \frac{1}{6}\).

b) \(\frac{3}{7} \cdot \frac{{ - 5}}{{12}} + \frac{3}{7} \cdot \frac{{ - 7}}{{12}} + \frac{{ - 4}}{7}\)

\[ = \frac{3}{7} \cdot \left( {\frac{{ - 5}}{{12}} + \frac{{ - 7}}{{12}}} \right) + \frac{{ - 4}}{7}\]

\[ = \frac{3}{7} \cdot \left( { - 1} \right) + \frac{{ - 4}}{7}\]

\[ = \frac{{ - 3}}{7} + \frac{{ - 4}}{7}\]

\[ = - 1\].