The figure above shows 5 walkways, R,S,T,U, and V, leading to and from a momument. Carlos will take one walkway to the mounment and will leave by a different walkway. From how many different pairs of these walkways can Carlos choose? For example, the pair starting with Walkway S and ending with Walkway V is different from the pair starting with walkway V and ending with Walkway S.
I used factorials to solve this problem instead of nCr because the problem says that order matters but I find that factorials doesn't make sense... i.e. 4x3x2x1. How to solve?