COMBINATIONS

Good greetings, friends and David :)

In class we have been studying about combinations. First things first you must become a expert on telling the difference between a permutation and a combination. The difference between permutations and combinations is:

         Permutation                                   Combinations
                 2 Actions:                                        1 Action:
                          1. Select                                           1. Select
                          2. Arrange                     *No dash method for combinations*
             
To tell the difference you must always ask yourself: "is the order important or not?".

Example 1: "How many can you select 2 fruits to eat if there are 12 to choose from"
- We are selecting 2 fruits from 12 options
- The order does not matter
- Therefore it is a combination

Example 2:"The combination to the safe is 472". 
- Now we do care about the order. "724" won't work, nor will "247". It has to be exactly 4-7-2.

Formula:

Example: Evaluate:

10C2

n = 10                      n! / r!(n-r)!                 

r = 2                        10! / 2!(10-2)!
                                10! / 2!(8)!        =  45