Question

Compute the permutation.

Answer 1

We have two slots A and B
Slot A has 4 choices (2,4,5,8)
Once we make a choice, we can't reuse it. So we have 3 choices left for slot B

Multiply out the values mentioned above to get: 4*3 = 12

Alternatively you can use the nPr formula to get
n P r = (n!)/(n-r)!
4 P 2 = (4!)/(4-2)!
4 P 2 = (4!)/(2!)
4 P 2 = (4*3*2*1)/(2*1)
4 P 2 = 24/2
4 P 2 = 12
yielding the same answer

So no matter which method you use, the final answer is 12