SOLUTION: Determine the number of combinations of 9 things taken 7 at a time.

Algebra ->  Permutations -> SOLUTION: Determine the number of combinations of 9 things taken 7 at a time.      Log On


   

Question 34558: Determine the number of combinations of 9 things taken 7 at a time.
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
9C7= [9!]/[(9-7)! * 71]
=[9*8]/[1*2]
Notice that 9C7 is the same as 9C2
In each case you have "9" to choose from.
9C7 means you are forming groups of size 7.
But that implies you are automatically forming groups of 2.
Therefore 9C7=9C2
Each one is simply 9*8/1*2=36
Cheers,
Stan H.