6. There are 10 equally spaced points on a circle. Then, among the convex quadrilaterals formed by choosing 4 of these 10 points, the ratio of trapezoids is $\qquad$
6. $\frac{2}{7}$.

Select any 4 points, there are $\mathrm{C}_{10}^{4}=210$ convex quadrilaterals, among which, the two parallel sides of a trapezoid can be chosen either from 5 sets of 5 parallel chords parallel to the diameter, or from 5 sets of 4 parallel chords not parallel to the diameter, excluding rectangles, there are 60 trapezoids in total.
Therefore, the ratio of the number of trapezoids is $\frac{2}{7}$.