00:01
The main thing is the difference between if order matters or it doesn't.
00:11
So the big thing there is what i call permutation.
00:15
And so in this problem you have 10 permutation 5.
00:19
And what that tells you then is that you do the first number factorial over, you subtract the two numbers.
00:25
I'm going to actually write that out because some people think that it's just the second number factorial.
00:31
That's not the case.
00:32
So in this problem, let me just move it down here.
00:38
It's 10 times 9 times 8.
00:40
That's how you do factorials.
00:43
And i'm going to stop at 5 factorial instead of writing it all down because you also have 5 factorial on bottom, which actually cancels out.
00:50
And you can then do the calculator 10 times 9 times 8 times 7 times 6.
00:55
And you get an answer of 30 ,240.
00:59
So what's different about if the order doesn't matter is it's what's called a combination.
01:06
And the difference there is you do the same thing as a permutation...