Out of how many people should a group at least consist in order to
have that the probability that two persons out of that group are having birthday on the same day, is larger than 1/2?
Show that there exist only five platonic solids (that are objects which are build out of the one sort of regular polygons, like the tetrahedron and the cube). Hint: use that for each solid in three dimensions it holds that the number of vertices + the number of faces is equal to the number of edges + 2.
