Question 144794
It depends.  Does the order of the group of 4 people matter?  Let's say your group of 9 consists of Alice, Bob, Carly, David, Ernest, Fran, Gillian, Henry, and Iris.  Clearly, Alice, Bob, Carly, and David is one set of 4 people that you could select.  The question is this:  Is Alice, Bob, Carly, and David different from David, Carly, Bob, and Alice?  If you were just selecting 4 committee members, then the order doesn't matter, but if you were selecting a Club President, Vice-President, Secretary, and Treasurer, then order would definitely matter.


So, if order matters, then you have a permutation of 9 things taken 4 at a time given by: {{{9!/(9-4)!}}}.  Here's a calculation shortcut:  {{{9!/(9-4)!=9!/5!=9*8*7*6*5!/5!=9*8*7*6}}}.  


If order does not matter, then you have a combination, and the answer you got for the permutation is too large by a factor of the number of ways that you can arrange the group of 4, namely 4!.  So you need to divide the permutation calculation by that amount:  The combination of 9 things taken 4 at a time is then: {{{9!/(4!(9-4)!)}}}.  Use the same calculation shortcut from above:


{{{9!/(4!(9-4)!)=9*8*7*6/(4*3*2)=3*2*7*2}}}.