Homework Help

How many combinations of 5 players can be created from a group of 9 players? How do I...

user profile pic

jdorry | Student, Undergraduate | eNotes Newbie

Posted January 21, 2009 at 3:07 AM via web

dislike -1 like

How many combinations of 5 players can be created from a group of 9 players?

How do I solve this problem?

Thanks for any help!

3 Answers | Add Yours

user profile pic

cburr | Middle School Teacher | (Level 2) Associate Educator

Posted January 21, 2009 at 12:26 PM (Answer #1)

dislike 1 like

There is a formula for this involving factorials.  A factorial is the starting number (A) times (A-1) times (A-2) etc down to A times 1.  The symbol for factorial is "!"  We use factorials for these problems, because they represent the number of combinations we can get from a group of numbers.

Let's say the total number in the group is X.  The size of each combination is Y.  

The formula for the number of combinations is:

X!  /  Y! (x-y)! 

In your problem, X=9 and y=5.  So, the formula works out to:

9 x 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1 / (5 x 4 x 3 x 2 x 1) times (4 x 3 x 2 x 1)

9! = 362880

5! = 120

4! = 24

Substituting these amounts, we get: 

362880 / 120 x 24

or

362880 / 2880

or

126 

user profile pic

revolution | College Teacher | Valedictorian

Posted July 24, 2010 at 10:48 PM (Answer #2)

dislike 0 like

You know there is a group of nine players so lets name it n players in total. You also know the size of each possible combination is 5 players, so lets give in r players in each combination.

For this problem, we are using a formula called a binomial coefficient and is denoted by nCr, which is n choose r.

The general equation is  n!/ r!(n-r)!

n!=9!

= n(n-1)(n-2)(n-3)....

= 9*8*7*6*5*4*3*2*1

= 362880

r!=5!

= r(r-1)(r-2)(r-3)...

= 5*4*3*2*1

= 120

(n-r)!= (9-5)!

= 4!

= 4*3*2*1

= 24

so, combination is= 362880/ 120*24

=  362880/ 2880

= 126 possibilities

user profile pic

kyouraku | Student, Undergraduate | eNoter

Posted July 25, 2010 at 5:35 AM (Answer #3)

dislike 0 like

uhh simple it's just 9C5= 9!/5!4!   != factorial i.e 5! = 5 x 4 x 3 x 2 x 1, 3!= 3 x 2 x 1

Join to answer this question

Join a community of thousands of dedicated teachers and students.

Join eNotes