Answer:
If the order doesn't matter then we have a combination, if the order do matter then we have a permutation. One could say that a permutation is an ordered combination.
a) When order matters, the total number of ways to select four cards is 9∗8∗7∗6: the 4-tuples are distinguished by content and/or by order. b) If the order does not matter then it will be (94): the 4-tuples are distinguished only by content. Our universe is given by all the sets {1≤x<y<z<w≤9}.
