This is a question of permutation and combination. The person who plays the Tang Priest can make one of the four people have four possibilities. Then the actor who plays the Monkey King can only choose one of the remaining three people. There are three possibilities; Playing Pig Bajie is one of the two remaining candidates. There are two possibilities. Finally, Friar Sand had no choice. One possibility, so there are always ***4*3*2* 1=24 kinds.

If calculated by the formula, it is: c (41) * c (31) * c (21) = 24.