Ta có: \(\left\{{}\begin{matrix}p+e+n=28\\p=e\\n=10\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}p=e=9\\n=10\end{matrix}\right.\)
Ta có: n + p + e = 28
Mà p = e, nên: 2p + n = 28
Đề cho n = 10
=> 2p + 10 = 28
<=> 2p = 18
<=> p = 9
Vậy p = e = 9