Q. You've said that two slot machines that look exactly the same can have different payback percentages. By exactly the same I assume you're including the payoffs. If I look up the payoffs for one machine, they'll be the same as the other. Then if both machines are using a random number generator, how can they have different percentages?

A. Let's make up a simple example, mapping symbols from a three-reel game onto a virtual reel, using a number set of only 100 numbers for each reel. On real slot machines, the numbers are a lot larger, and the math that goes into a playable game is more complex, but this will do for an illustration.

Let's say that on the low-paying machine, you have a top jackpot of \$10,000, and you want it show up an average of once per 1 million spins. Then of the 100 numbers that the RNG has to work with, I could assign one per reel to the jackpot symbol. In essence, I'd tell the game program, "Every time the RNG spits out No. 1, stop on the jackpot symbol for the corresponding reel." If I do this the same way for each reel, then the chances of hitting a top jackpot are 1 in 100x100x100, or 1 in 1 million.

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Now let's say I wanted a looser game that paid twice as many big jackpots. Then I could tell the game program, "Every time the RNG spits out No. 1 for the first reel, stop on the jackpot symbol. Every time it spits out No. 1 for the second reel, stop on the jackpot symbol. And stop on the jackpot symbol every time it stops on No. 1 or 2 for the third reel."

Now it's stopping on the jackpot symbol on the third reel once per 50 spins instead of once per 100. My top jackpot odds are 1 in 100x100x50, or 1 in 500,000. It has the same pay table, but it's paying out the jackpot twice as often and, if all else is equal through the rest of the mapping, it has a higher payback percentage.

The games look identical, results are random, but they have different percentages.

Q. I was playing \$25 blackjack, flat bets. I don't count like my husband, I just play basic strategy. After a couple of hours I asked a pit supervisor if I could get a coffee shop comp. He said I didn't qualify, and I asked how much more I'd have to play. He said, "Honey, you could sit there all night and I wouldn't write you a coffee shop comp." The rudeness aside, does that seem right to you?

A. In a pure dollars-and-cents proposition, your value to the house depends both on the speed of the game and the casino's perception of your skill as a player.

Let's look at two speed assumptions. If you're playing at a full table moving at 50 hands an hour, a \$25 player is risking \$1,250 an hour. If there are empty spots and you're playing 150 hands an hour, then you're risking \$3,750.

Next comes the player's skill. I used to have operators tell me they assumed a 2 to 2.5 percent edge over average players. In an era of tightening comps, I had one operator tell me he assumed only a 1 percent edge.

With a 2 percent assumption, your theoretical value to the casino is \$25 an hour at the slow table, and \$75 at the fast one. With a 1 percent assumption, those drop to \$12.50 and \$37.50.

But if the supervisor had you pegged as a basic strategy player, he could even have dropped assumption of half a percent, giving you a theoretical value of \$6.25 or \$18.75.

If you're pegged as a basic strategy player at a slow table, after two hours the house would see its theoretical win at \$12.50. Casinos used to rebate anywhere from 10 to 40 percent of that in comps, but now comp levels cluster toward the low end. At 10 percent, it would see you as worthy of \$1.25 an hour in comps, and it would take a LONG time to earn a trip to the coffee shop.

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