Cho 

- Hướng dẫn giải

Đáp án cần chọn là: B

$\begin{array}{l}A=\frac{\mathrm{36.85.20}}{\mathrm{25.84.34}}\\ =\frac{\mathrm{6.6.17.5.4.5}}{\mathrm{5.5.6.2.7.17.2}}\\ =\frac{{\mathrm{6.6.17.4.5}}^2}{{\mathrm{7.6.17.4.5}}^2}=\frac{6}{7}\\ B=\frac{\mathrm{30.63.65.8}}{\mathrm{117.200.49}}\\ =\frac{\mathrm{6.5.7.9.13.5.4.2}}{\mathrm{13.9.20.10.7.7}}\\ =\frac{\mathrm{6.7.10.20.9.13}}{\mathrm{7.7.10.20.9.13}}=\frac{6}{7}\end{array}$

Suy ra A = B.