Here’s a repost from many years ago. I have no idea how to do it or what the answer is.
A boy has four red blocks and eight blue blocks. He arranges the twelve blocks uniformly randomly, in a ring.
What is the probability that no two red blocks are next to each other?
As I strongly suspect that combinations are involved, use C(n,r) = n! / ((n-r)! r!) for consistent notation.