using c/ to find probablity

[pokerpairs]

Many of the probabilty posts use a formula wiht c in it. Could you please explain how it works; I can not find the function on my TI-83 Plus calculator. I was also wondering if it could be used at the table without a calculator. Any description that would help me use it would be great.
Thanks

[aloiz]

C(X,Y) is counting the number of combinations of group Y that can be made from group X. Spoken as "X choose Y". Mathmatically it's equivilant to X!/( (X-Y)! * Y! ). Excel has a function call COMBIN that computes these. I know the TI-89 has a function something like nCr, but I'm not sure the 83plus has one.

aloiz

[pokerpairs]

Aloiz , thanks for the reply but it is still a little fuzzy to me. Do I have to have the function c to solve questions like the probability of an overpair?

[aloiz]

No you don't always have to use combinations to solve those type of probability questions, but it makes things easier.

Here's a simple example. You're heads up preflop, and you have pocket tens. What is the probability that your opponent has an overpair?
What we want is the total number of ways he can have an overpair divided by the the total number of possible two card hands he could have.

Total number of hands that give our opponent an overpair = 4 * C(4,2). There are 4 pairs higher than T, and each pair can be dealt out C(4,2) distinct ways e.g. AsAh, AsAd, AsAc, AhAd, AhAc, AdAc. C(4,2), or four choose two is equal to 4!/( (4-2)! * 2! ) = 6. So it's just an easy way to count up the number of distinct groups from a larger group of n distinct objects.

Total number of two card hands given that we hold two tens = C(50,2) = 1225.

take 4 * C(4,2)/C(50,2) to get our final answer of .0196

aloiz

[ChromePony]

I have a TI-82 that has this function so I imagine an 83 would too, im not sure how similar they are but look under the MATH menu, its like nCr....at least it is on the 82. Hope this helps.

[uuDevil]

Check out this page-- 3rd example down. (http://www.mtsu.edu/~math141/counting.html)

But you definitely DO NOT want to use this at the table. Play with probabilities away from the table. Memorize the (few) important numbers-- you can find these in any good poker book.