\(a,N=\dfrac{M}{300}=\dfrac{9.10^5}{300}=3000\left(Nu\right)\\ b,Ta.có:\left\{{}\begin{matrix}A+G=\dfrac{N}{2}=1500\\A=\dfrac{2}{3}G\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}A=T=600\left(Nu\right)\\G=X=900\left(Nu\right)\end{matrix}\right.\\ \left\{{}\begin{matrix}\%A=\%T=\dfrac{600}{3000}.100\%=20\%N\\\%G=\%X=50\%N-20\%N=30\%N\end{matrix}\right.\\ c,C=\dfrac{N}{20}=\dfrac{3000}{20}=150\left(vòng\right)\)