Mark M. answered 12/01/14
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This is a combination because the order does not matter, i.e. Joe, John, Jack, and Josh is the same committee as
John, Joe, Josh, and Jack.
18C4 = 18 · 17 · 16 · 15 / 4 · 3 · 2 · 1
18C4 = 3060
Three thousand sixty different committees could be selected.