3 bài này em làm được bài nào chưa?
Bài thứ 2:
\(a,\\ \left\{{}\begin{matrix}P+N=34\\P+N=68\%.\left(34+E\right)\\P=E\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}P+N=34\\E=\dfrac{34}{68\%}-34=16\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}P=E=16\\N=18\end{matrix}\right.\\ b,P+E=16+16=32\left(HẠT\right)\)
BTBS2:
\(\left\{{}\begin{matrix}P+E+N=32\\\left(P+E\right)=62,5\%.32=20\\P=E\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2P+N=32\\P=E=\dfrac{20}{2}=10\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}P=E=Z=10\\N=12\end{matrix}\right.\\ \Rightarrow A=Z+N=10+12=22\left(đ.v.C\right)\)
