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?
+2862 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.
+2862 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.
