Answer:
nPr = n!/(n-r)!
Explanation:
The equation for permutations:
nPr = n!/(n-r)!
Where,
n = total number of objects
r = number of objects selected
The order of the elements matter with permutations.
For example,
A four digit code could be anything between 0000 to 9999, but each digit can be used once. There are 10 numbers (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) and are looking for 4 digits. n = 10, r = 4.
Giving us the equation, 10!/(10-4)!
10! = 10 * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1
10 - 4 = 6; 6!
6! = 6 * 5 * 4 * 3 * 2 * 1
(10 * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1) / (6 * 5 * 4 * 3 * 2 * 1)
10 * 9 * 8 * 7 = 5040