Theo đề ta có:
\(hpt:\left\{{}\begin{matrix}p+e+n=40\\n-e=1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2p+n=40\\-p+n=1\end{matrix}\right.\Leftrightarrow3p=39\Leftrightarrow p=13\Leftrightarrow\left\{{}\begin{matrix}p=e=13\\n=1+p=13+1=14\end{matrix}\right.\)
Theo đề bài, ta có:
2p + n = 40
n - p = 1
<=> p = e = 13 ; n = 14