1. Thực hiện phép tính (tính nhanh nếu có thể): a) 2/15 +- 4/3;5/6;2. Tìm x: a) x + 1/3 = 5/12; 

1.

a) \[\frac{2}{{15}} + \frac{{ - 4}}{3}:\frac{5}{6}\]\[ = \frac{2}{{15}} + \frac{{ - 4}}{3}.\frac{6}{5}\]\[ = \frac{2}{{15}} + \frac{{ - 24}}{{15}} = \frac{{ - 22}}{{15}}\];

b) \[4\frac{3}{5} + \frac{2}{5}.\frac{{ - 23}}{{16}} - \frac{{14}}{{35}}:\frac{{ - 16}}{7}\]\[ = \frac{{23}}{5} - \frac{{23}}{{5.8}} + \frac{{14}}{{35}}.\frac{7}{{16}}\]

\[ = \frac{{23}}{5} + \frac{{ - 23}}{{5.8}} + \frac{7}{{5.8}}\]\[ = \frac{{23}}{5} + \frac{{ - 16}}{{5.8}}\]\[ = \frac{{23}}{5} + \frac{{ - 2}}{5}\]\[ = \frac{{21}}{5}\].

2.

a) \[x + \frac{1}{3} = \frac{5}{{12}}\] \[x = \frac{5}{{12}} - \frac{1}{3}\] \[x = \frac{5}{{12}} - \frac{4}{{12}}\] \[x = \frac{1}{{12}}\] Vậy \[x = \frac{1}{{12}}\].

b) \(\frac{2}{3}x + \frac{1}{2}x = \frac{{15}}{{12}}\) \(\left( {\frac{2}{3} + \frac{1}{2}} \right)\,\,.\,\,x = \frac{{15}}{{12}}\) \(\frac{7}{6}x = \frac{{15}}{{12}}\) \(x = \frac{{15}}{{12}}:\frac{7}{6}\) \(x = \frac{{15}}{{14}}\). Vậy \(x = \frac{{15}}{{14}}\).