Theo bài và NTBS ta có: \(\left\{{}\begin{matrix}\%A-\%G=20\%\\\%A+\%G=50\%\end{matrix}\right.\rightarrow\left\{{}\begin{matrix}\%A=35\%\\\%G=15\%\end{matrix}\right.\)
\(\rightarrow\left\{{}\begin{matrix}A=T=35\%N=1050\left(nu\right)\\G=X=15\%N=450\left(nu\right)\end{matrix}\right.\)
\(\rightarrow L=3,4.\dfrac{N}{2}=5100\left(\overset{o}{A}\right)\)