The only math a player should know is how to calculate what he feels his outs are, and correlate that into a percentage rather quickly. The system I found that works best is this - take your outs, let's says for this example it's a flush draw we hold.
A/A no hearts
Flop: Ks 2h 6h
This means we have 9 outs (the nine hearts left in the deck). Take your outs (in this case we have 9), multiply by 2 and add 1. So we have 9 x 2 = 18 + 1 = 19% chance of hitting our draw on the turn. In order to figure out what our odds are for the turn AND river; just double the 19% to 38% to compensate for the extra card. This gives you the chances of hitting your draw if you play the hand to a showdown.
This works for any scenario too. So if you can somehow narrow down what you think your opponent has (in this case if my opponent bet into me I would assume he has A/K for the purposes of making a pot odds
decision); you can assume your percentage to win the hand using this system. Which generally leads to good decisions with regards to how much money you should be investing relative to your odds of winning. If I'm 38% to win with my draw, then I don't really want to put more than another 38% investment. So if the pot is 300 and the bettor comes out with a bet of 100 ... I'd call, b/c I'm getting 4 to 1 odds now after he makes the pot 400 with his bet. And b/c I'm better than 4 to 1 to win the hand, I call. So even though you know you're probably losing the hand at the moment, you just made a great call. Once you know the math poker is less stressful, ironic as that seems.
Again - Outs x 2 + 1 = percentage to hit on next card
Also - (Outs x 2 + 1)x2 = percentage to win on showdown if you see both the turn and river card