The Math Of Poker

Although it may not be good to be known as a math player, you have to know math to be a good player.
There are 2 key formulas to use in Texas Hold 'em to help determine your odds.
The first is known as the Rule Of 4.  After the flop is down, you can calculate the number of outs you have by multiplying the amount of outs by 4%, or 0.04.  For example, lets say you hold JcJs, with $100 in the pot, then the flop comes Qd, 6s, 7c.  If your opponent checks, should you raise?  That is a question that you must determine based on his playing style and other factors.  But lets say your opponent raises $50, half the pot..  For this pot to be worth calling, you need to do some math.  In this case it is simple, as your only real outs are at least one of the 2 remaining Jacks.  Your opponent could have pocket Qs, Ks, Q7, 67, As, a small pocket pair, rags, or even Jacks like you, but there is really nothing to go off of.  Hence the math:  You must multiply the number of outs (outs are the cards that can bring you a better hand such as a set, straight, flush, etc; in this case, 2) by 4%.  This means that you have an 8% chance of hitting another J on either the turn or the river, so the pot needs to be paying odds of about 10 to 1 for it to be a smart call.  In this case, the odds are 3 to 1, so it is wise to fold, all other things equal.
Now under the same circumstances, lets say that the turn comes and it is a 5d so the board is looking like Qd, 6s, 7c, 5d.  In this same scenario, to calculate the chances of making a Jack on the Turn (assuming that the flop was either checked or the odds were good) you must multiply the number of outs (still 2) by 2%, meaning that there is a 4% chance of hitting a J on the river.  The pot must now be paying 20 to 1 odds, so if the pot is currently at $100, the biggest bet you can call is $5.
Hopefully that clears up some questions of math in poker, but if not, drop a comment!!