Cách 1 : \(M=\frac{10}{5}.\frac{5}{7}+\frac{15}{5}.\frac{5}{7}=\frac{10}{7}+\frac{15}{7}=\frac{25}{7}\)
Cách 2 : \(M=\frac{8}{5}.\frac{5}{7}+\frac{2}{5}.\frac{5}{7}+\frac{6}{5}.\frac{5}{7}+\frac{9}{5}.\frac{5}{7}\)
\(=\frac{8}{7}+\frac{2}{7}+\frac{6}{7}+\frac{9}{7}=\frac{25}{7}\)
Cách 3 : \(M=\left(\frac{8}{5}+\frac{2}{5}+\frac{6}{5}+\frac{9}{5}\right).\frac{5}{7}=\frac{25}{5}.\frac{5}{7}=\frac{25}{7}\)