Three vertices are chosen randomly from the seven vertices of a regular 7-sided polygon. The probability that hey form the vertices of an isosceles triangle is:
I know that the this problem deals with geometry and combinations. I just drew its picture and from it I think that from a single vertex of the polygon 5 isosceles triangles can be drawn. So, is 7*5=35 the no. of isosceles triangles that can be drawn?