Permutations
For permutations ORDER MATTERS! Lets say 4 people (A,B,C,D) are sitting in four chairs. How many different ways can they arrange themselves and not repeat an arrangement? As you can see there are 6 groupings with A in the first position. For the second column B is in the first position. Then C and D take their turns being in the first chair. The answer is 24 arrangements. This can also be done by doing 4!. (4! means Factorial) Watch the video to learn how to use the permutations formula.
Factorial - a multiplication count down. Start with the number given and count all the way down to 1. 4! = 4x3x2x1 = 24 5! = 5x4x3x2x1 = 120 6! = 6x5x4x3x2x1 = 720 |
Combinations
For Combinations ORDER DOES NOT MATTER! You are more concerned about the number of people or objects involved instead of the arrangement of the group.
Let's say you have 3 friends but you can only take 2 to the upcoming concert. How many different ways can you select 2 friends from a group of 3? If you had 3 friends (Blue, Red, and Green), then you could take: (Blue with Red) or (Blue with Green) or (Red with Green). The answer is 3 ways. Watch the video to find out more. |
|
|
Khan Academy
|
|
|
|
|
|