# ACT Math : How to find permutation notation

## Example Questions

### Example Question #13 : Permutation / Combination

In permutation notation, what does 8P4 represent?

6720

336

1680

210

1680

Explanation:

The expression  8P4 represents the number of permutations of 8 objects arranged 4 at a time. Thus, 8 x 7 x 6 x 5 = 1680

### Example Question #2 : How To Find Permutation Notation

How many different ways can five books be lined up on a shelf?

100

80

120

150

60

120

Explanation:

Order matters, so we use permutations:  (5)(4)(3)(2)(1) = 120

There are five possibilities for the first book, four possibilities for the second book, three for the third, and two for the fourth, and one possibility for the last book.

### Example Question #1 : How To Find Permutation Notation

How many different ways can cheese slices be stacked in piles containing  unique types if you are presented with a selection of  different cheeses?  (Presume that the order of the cheese slices does matter.)