Compute the permutation.

How many different positive integers of 2 digits each can be made with the digits 2, 4, 5, and 8, if no digit is repeated in a number?

Answers:

8

12

16

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