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A club has 15 members and needs to choose 2 members to be co-presidents. In how many ways can the club choose its co-presidents?

 Apr 28, 2019

Best Answer 

 #1
avatar+491 
+2

Since you are choosing 2 out of 15, you use the formula \(\frac{n!}{r!(n-r)!}\), which is the combination formula

 

N represents number of items you are choosing out of, and r represents the number of items you are choosing.

 

Substituting in you will get 105 ways.

 

 

Whenever a problem is asking you to choose a certain number of items out of a total number of items, then use the formula above.

 Apr 28, 2019
edited by CalculatorUser  Apr 28, 2019
 #1
avatar+491 
+2
Best Answer

Since you are choosing 2 out of 15, you use the formula \(\frac{n!}{r!(n-r)!}\), which is the combination formula

 

N represents number of items you are choosing out of, and r represents the number of items you are choosing.

 

Substituting in you will get 105 ways.

 

 

Whenever a problem is asking you to choose a certain number of items out of a total number of items, then use the formula above.

CalculatorUser Apr 28, 2019
edited by CalculatorUser  Apr 28, 2019

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