Which of the following are in descending order of their value ?

Converting each of the given fractions in to decimal form, we get
$$\eqalign{ & \frac{1}{3} = 0.33 \cr & \frac{2}{5} = 0.4 \cr & \frac{3}{7} = 0.42 \cr & \frac{4}{5} = 0.8 \cr & \frac{5}{6} = 0.83 \cr & \frac{6}{7} = 0.85 \cr} $$
Clearly, 0.85 > 0.83 > 0.8 > 0.42 > 0.4 > 0.33
So, $$\frac{6}{7}$$ > $$\frac{5}{6}$$ > $$\frac{4}{5}$$ > $$\frac{3}{7}$$ > $$\frac{2}{5}$$ > $$\frac{1}{3}$$