Permutations

Well this is an definitely a new way of learning, I learned quite a few things just by researching and doing this, and I hope I can learn just as easily for combinations... Sorry for any repeats. That's all.

Definition: A permutation is a set of objects that are arranged in a certain order, where the order is important.

Formula:

n is the total number of objects ; r is the number of objects chosen .
Examples:

Number 1:

You want to know how many orders your cd player will play your 13 song cd, on shuffle mode. At first there is a one in fourteen chance that any song will be played. The next song only has 1 in 12 chance of being played, because there are only 13 songs left to be played. The possibility of outcomes of a song being played decreases by one each time. The following will be the used formula.
P(n) = 13!
OR
P(n) = 13*12 * 11 * 10 * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1 =6227020800 ways of playing the same CD, in different orders.

Number 2 (from Webct learning)
How many five-letter "words" can be made from the alphabet if no letters are repeated? A "word" in this case is any five-letter arrangement with all letters different.

Solution:We will use the formula to answer this question.

The value of 'n' is 26 (there are 26 objects to choose from) and the value of 'r' is 5 (we pick five letters).


The formula may be convenient to use, but it is not essential. You can always find the number of arrangements (permutations) by multiplication as shown below.



Links
Permutations Calculator
Easy Permutations
More Examples