Tính: ​\(\dfrac{6}{{15}} + \dfrac{{12}}{{ - 15}}\)​

* Hướng dẫn giải

Ta có:

\(\begin{gathered}
  \frac{6}{{15}} + \frac{{12}}{{ - 15}} = \frac{6}{{15}} + \left( {\frac{{ - 12}}{{15}}} \right) \hfill \\
   = \frac{{6 + \left( { - 12} \right)}}{{15}} = \frac{{ - 6}}{{15}} \hfill \\
   = \frac{{ - 2}}{5} \hfill \\ 
\end{gathered} \)