March 27, 2017

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i just need help with factorials

I assume you know what a factorial is:
1! = 1
2! = 1x2 = 2
3! = 1x2x3 = 6
N! = 1x2x3x...x(N-1)xN

They occur often in probability theory.

Please ask a more specific question about factorials. I have no idea what else to tell you.

what is the explicit formula for the nth factorial? is there one without n*(n-1)*(n-2) and so forth?

No, drwls is correct; N! = 1*2*3...*N.

However, when using factorials, short-cuts and simplifications will often be present. For example, the formula for counting the number of ways one can deal two cards from a standard 52-card deck is:
52! / 2!(52-2)!

Well, calculating 52! by itself is an onerous task. However, we can simplify. 52!/50! cancels to 51*52, and 2! is simply 1*2=2. So, the answer is 51*52/2 = 1326.

I hope this helps

Why is 0! equal to one? write back asap!!
-concerned student seeking help

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