While playing a card game with my nephew, he asked about shuffling the cards.
Let's say I am playing a card game and the stack of cards is shuffled between each game. (note - the cards must all be face down)
What is the total number of different ways the cards can be stacked?
I wrote on piece of paper 52! and explained the multiplication to him and plugged it into the iPhone calculator. The answer seemed to be a bit large, so I decided to open a question here.
Thanks
The way you have to see this is the following.
First you should look at wheater this is a combination, or a permutation. The usual way to do this is to ask "Does Order matter?" (i.e you have to ask yourself if having a queen of diamonds at the bottom of your stack is the same as having a king of hearts at the bottom of your stack ? Are these two stacks the same ? The answer is no, they're not the same). Thus, this is a permutation.
Second, you should ask yourself: "Is repetition allowed ?" (i.e can you have, for example, two queen of hearts in your stack? Again, you cannot, so repetition is not allowed).
The formula for permutation without repetition (a.k.a permutation without replacement) is the following: $$P(n,r) = \frac{n!}{(n-r)!}$$ where $n$ is the number of cards you can pick (you have a total of $52$ cards), and $r$ is the number of cards you are picking (and stacking).
In your case, you have $n=52$ cards and you are stacking $r=52$ cards (you're stacking all of them), so you have: $$P(52,52) = \frac{52!}{0!}\\=52!$$ (note that $0! = 1$)
Thus the answer to your question is $52!$ (assuming your cards cannot be upside down).
Now, say that instead of stacking all the cards, you want to know how many stacks of $7$ cards you can make with one deck (i.e a total of $52$ cards), then the answer is simply $P(52,7)$.