[tex]\frac{9}{35}\cdot\frac{\not7^1}{16}\cdot\frac{20}{\not21_3}=\frac{9}{35}\cdot\frac{1}{\not16_4}\cdot\frac{\not20^5}{3}=\frac{\not9^3}{35}\cdot\frac{1}{4}\cdot\frac{5}{\not3_1}=\frac{3}{\not35_7}\cdot\frac{1}{4}\cdot\frac{\not5^1}{1}\\\\=\frac{3}{7}\cdot\frac{1}{4}\cdot\frac{1}{1}=\frac{3\cdot1\cdot1}{7\cdot4\cdot1}=\frac{3}{28}[/tex]
