Ta có hệ :\(\Leftrightarrow\left\{{}\begin{matrix}P+N=39\\\frac{2P}{N}=\frac{19}{10}\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}P+N=39\\20P-19N=0\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}P=19\\N=20\end{matrix}\right.\)