A,-1/3+4/5 b, (-2/7+5/6):5/12+(-5?7 +1/6):5/12

Đáp án:

$\begin{array}{l}
a)\\
 – \frac{1}{3} + \frac{4}{5} = \frac{{ – 5}}{{15}} + \frac{{4.3}}{{15}} = \frac{{ – 5 + 12}}{{15}} = \frac{7}{{15}}\\
b)\\
\left( {\frac{{ – 2}}{7} + \frac{5}{6}} \right):\frac{5}{{12}} + \left( { – \frac{5}{7} + \frac{1}{6}} \right):\frac{5}{{12}}\\
 = \frac{{ – 2.6 + 5.7}}{{42}}.\frac{{12}}{5} + \frac{{ – 5.6 + 7}}{{42}}.\frac{{12}}{5}\\
 = \frac{{23}}{{42}}.\frac{{12}}{5} + \frac{{ – 23}}{{42}}.\frac{{12}}{5}\\
 = 0
\end{array}$