1. Lesson 2.9 Objective: Probability permutations and combinations
Counting principal
Example: Suppose you are picking out an outfit for a job interview. You have three pairs of shoes to choose from, four pairs of pants, and 2 shirts. How many different outfits can you put together using an item from each category?
3 shoes •
4 pants •
2 Shirts
# of Outfits =
3 • 4 • 2= 24 different outfits

2. Permutations (when the order matters)
Example: Six people are running in a race. The top three places get 1st, 2nd, and 3rd prize. How many arrangements are there?
How many people have a shot at….
1st
2nd
3rd 4 = 6 • 5 •
120 arrangements

3. Combinations:
When the order does not matter
Six People are running for city council. There are three positions available. How many combinations are there?
Hint Use A,B,C,D,E,F for the six candidates
Mathematically
ABC
ACF
BDE
BDF
ABD
ADE
120
= 20
BEF 6
ABE
ADF
CDE
ABF
AEF
CDF
ACD
BCD
When the order does not matters, you must divide!
CEF
BCE
ACE
BCF
DEF
20 DIFFERENT COMBINATIONS
On test!!!!!

4. Example: You just bought 5 books and want to take two of them with you on vacation. How many different combinations of two books can you take?
Hint: Use A,B,C,D,E for each book AB BC CE
MATHEMATICALLY AC BD DE AD BE 20
= 10 2 AE CD
10 COMBINATIONS