Permutations (SAT math section)

Discus: SAT/ACT Tests and Test Preparation: April 2004 Archive: Permutations (SAT math section)
 By Brum (Brum) on Friday, April 30, 2004 - 09:38 pm: Edit

Can someone please give an example and/or explain how to use permutations for probability and when you would use it?

 By Crypto86 (Crypto86) on Friday, April 30, 2004 - 09:43 pm: Edit

An example (in a 10 REAL practice test) would be:

There are 3 cars A,B,C and 4 empty parking spaces. How many different arrangements are there in parking these cars (including the empty space).

Here, order matters in parking the cars (it's like organizing a set of encyclopedia books - it matters if A is before B and vice versa).

So here, you could make the 4th parking space an "object" and you have 4 objects. The permutation arrangement of n objects is n! - so 4! = 4*3*2*1 = 24

Or you could use 4 nPr 3 (4 total choices [spaces] and 3 cars per different arrangement), which also equals 24.

That's the easiest and quickest example I could think of that I've seen on the SAT practice tests.