permutations and combinations

Question

How many four letter permutations can be formed from the first five letters of the alphabet?

Answer 1

Given the first five letters: A, B, C, D, E, we want to create as many “permutations” (combinations but order matters) as possible. Using the definition of permutation of “n” things taken at “r” times; P(n,r) = (n!) / (n-r)! Where “!” means factorial. (Factorial of X is X! = (X)(X-1)(X-2)...(1)).

Number of Permutation = 5! / (5-4)! = 5! / 1! = 5! = 5*4*3*2*1 = 120