In probability, the number of ways of arranging objects could be done in combinations and permutations. The only difference between them is if you arrange them with or without repetition. If you choose permutation, then the arrangement should have no repetition. Thus, for permutation, the number of ways of arranging 'r' things out of a total of 'n' objects is:
P = n!/(n-r)!, where the term '!' is called factorial
For example, when you say 8!, that would mean 8×7×6×5×4×3×2×1 = 40,320. Substituting the values:
P = 8!/(8-5)! = 6,720 ways