\(M=\frac{8^{20}+4^{20}}{4^{25}+64^5}=\frac{4^{20}.\left(2^{20}+1\right)}{4^{25}+\left(4^3\right)^5}=\frac{4^{20}.\left(2^{20}+1\right)}{4^{25}+4^{15}}\)
\(=\frac{4^{20}.\left(4^{10}+1\right)}{4^{25}.\left(4^{10}+1\right)}=\frac{1}{4^5}=\frac{1}{1024}\)