Permutations and Combinations
Lesson 6-7
Additional Examples
Algebra 2
In how many ways can 6 people line up from left to right for a
group photo?
Since everybody will be in the picture, you are using all the items from the
original set. You can use the Multiplication Counting Principle or
factorial notation.
There are six ways to select the first person in line, five ways to select the
next person, and so on.
The total number of permutations is 6 • 5 • 4 • 3 • 2 • 1 = 6!.
6! = 720
The 6 people can line up in 720 different orders.
Permutations and Combinations
Lesson 6-7
Algebra 2
Additional Examples
How many 4-letter codes can be made if no letter can be used
twice?
Method 1: Use the Multiplication Counting Principle.
26 • 25 • 24 • 23 = 358,800
Method 2: Use the permutation formula. Since there are 26 letters
arranged 4 at a time, n = 26 and r = 4.
26P4 =
26!
= 26! = 358,800
(26 – 4)!
22!
There are 358,800 possible arrangements of 4-letter codes with no duplicates.
Permutations and Combinations
Lesson 6-7
Additional Examples
Evaluate 10C4.
10!
10C4 = 4!(10 – 4)!
10!
= 4! • 6!
10 • 9 • 8 • 7 • 6 5 4 3 2 1
= 4•3•2•1• • • • • •
6• 5• 4• 3•2•1
10 • 9 • 8 • 7
= 4•3•2•1
= 210
Algebra 2
Permutations and Combinations
Lesson 6-7
Algebra 2
Additional Examples
A disk jockey wants to select 5 songs from a new CD that
contains 12 songs. How many 5-song selections are possible?
Relate: 12 songs chosen 5 songs at a time
Define: Let n = total number of songs.
Let r = number of songs chosen at a time.
Write: n C r = 12 C 5
Use the nCr feature of your calculator.
You can choose five songs in 792 ways.
Permutations and Combinations
Lesson 6-7
Algebra 2
Additional Examples
A pizza menu allows you to select 4 toppings at no extra
charge from a list of 9 possible toppings. In how many ways can you
select 4 or fewer toppings?
You may choose
4 toppings, 3 toppings, 2 toppings, 1 toppings, or none.
9C4
9C3
9C2
9C1
The total number of ways to pick the toppings is
126 + 84 + 36 + 9 + 1 = 256.
There are 256 ways to order your pizza.
9C0
Algebra 2
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