4.
Ta có: \(\left\{{}\begin{matrix}p+e+n=36\\p=e\\p+e=2n\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}p=e=12\\n=12\end{matrix}\right.\)
5.
Ta có: \(\left\{{}\begin{matrix}p+e+n=40\\p=e\\p+e-n=12\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}p=e=13\\n=14\end{matrix}\right.\)
4.
\(\left\{{}\begin{matrix}P+N+E=36\\P=E\\\dfrac{1}{2}\left(P+E\right)=N\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2P+N=36\\P=N\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}P=E=Z=12\\N=12\end{matrix}\right.\)
5.
\(\left\{{}\begin{matrix}P+N+E=40\\\left(P+E\right)-N=12\\P=E\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2P+N=40\\2P-N=12\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}P=E=Z=13\\N=14\end{matrix}\right.\)