The number of possible permutations of n items is n. Each of the different groups or selections which can be formed by taking some or all of a number of objects is called a combination. N P r n r.
Using the formula for permutations P n r n n - r that can be substituted into the above formula.
Here are rapid and easy tips and tricks and shortcuts on Permutation. NPr P n r n n-r. This is denoted by n P r. N n 1 n 2 n 3.