Bài 1:
\(\left\{{}\begin{matrix}P+N+E=56\\\left(P+E\right)-N=20\\P=E\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2P+E=56\\2P-E=20\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}P=E=Z=19\\N=18\end{matrix}\right.\)
Bài 2:
\(\left\{{}\begin{matrix}P+N+E=37\\P=E\\N=35,1351\%.37=13\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2P+N=37\\N=13\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}P=E=Z=12\\N=13\end{matrix}\right.\)