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Ask the Slot Expert: How bet size can legally affect chances for a bonus on a slot machine

11 April 2018

Question: We've always wondered how it works when a machine says, "Higher Bet Improves Chances for Bonus."

For example, Triple Quick Hits has three games going plus the moneybags on the side. Something must change in the programming in order to give you more chances at the bonus. I know machines only have one RNG, so we assume the "mapping" to the number of possible combinations must change. Or is it possible for a machine to have multiple RNGs? One that triggers the bonus, and another for the actual game. Either way, the machine has to know what level you're betting at.

Answer: We have to separate the base game — the spinning reels — from the additional game features.

The program running the slot machine makes 15 calls to the RNG, one for each reel in each game. It uses those numbers to determine where each reel will stop. This part of determining the game outcome is not affected by the number of coins bet other than whether enough was bet to enable each separate game, if playing fewer than all three games is possible — it's been a long time since I've played this machine so I don't remember.

Now it's time to figure out whether the moneybag free spins bonus will be triggered. The program probably makes one call to the RNG for each moneybag. Because this isn't the base game and the program has already determined where the reels will stop, the program can use different weightings based on the bet. Just to make up some numbers, there might be only a 10% chance of lighting up a moneybag at the minimum bet, but a 25% chance at the highest bet. You can actually get a good estimate of the probability of lighting up a moneybag by playing about 100 spins at each bet level and keeping tallies of how many times each moneybag is lit.

So the machine does not necessarily have separate RNGs for the base game and the bonus, but the program does make separate polls of the RNG to determine where the reels stop and whether a moneybag is lit and, thus, whether the bonus is triggered.

Machines can have multiple RNGs. In Nevada, regulations require that any randomly determined element that is not part of the game outcome must use a separate RNG. The example given in the technical documentation is the Quick Pick function on a Keno machine. The machine must use a separate RNG to choose the numbers that will be played and another RNG function to choose the numbers that are drawn in the actual game.

Multiple RNGs can also be used in the determination of the game outcome. In The Art of Intrusion, Kevin Mitnick describes how one group of cheats used a mistake made by the programmers of a video poker machine to cheat those machines. These machines used two RNGs to determine the cards that are dealt. The output from one RNG is added to the output of the other, then scaled down to the range 1 to 52 to select a card. That's all well and good and using two RNGs makes it difficult for RNG cheats to beat a machine.

But the programmers made one mistake. The right way to do it is to poll each RNG for each card. The programmers, however, polled one of the RNGs only at the start of each hand and used the same value for this RNG to select each card needed for the hand.

Oops. The cheats were able to beat these machines after they analyzed the program running the machine and figured out how the RNGs worked and were used.

Manufacturers are famously tight-lipped about revealing details of their RNG functions and how game outcomes are determined. The secrecy is not because of some vast conspiracy among the manufacturers to hide the ways that machines cheat players. No, the manufacturers don't give out the details because cheats will use all of the information they can get their hands on to figure out ways to cheat machines.


Question: All I know is that no matter how my times I hit 88 Fortunes, I always get $40 no matter how much money I'm betting. It's a scam. Who do we write to? It needs to be investigated why they never show you the board .

Answer: The investigation is closed. I can tell you why they don't reveal the coins that you didn't pick.

They don't reveal those coins because then you'd see that it was never possible to get any of the progressives other than the one you won. When the bonus is initiated, the machine polls the RNG to determine which progressive you will win. A few readers have written to say that they won the big progressive on a minimum bet, so each progressive is winnable at any bet level.

After the program uses the RNG to determine your progressive, it puts two coins on the screen for each of the progressives you can't win, and fills the other six positions with coins for your progressive. If you pick right, you can get two coins for each progressive and think that you have in 1-in-4 chance of hitting the big one. That's fun and exciting. But in reality, there's only one progressive you can win. Your next pick will reveal that progressive.

The machine could just display a message indicating which progressive it chose for you, but that wouldn't be much fun for a bonus round. There are plenty of entertaining ways to reveal a predetermined outcome, such as a spinning arrow that stops on one of the progressives, but the pick-'em way gives something for the player to do in the bonus round. Newer machines with this same sort of pick-'em bonus have a statement in the help screens saying that player interaction during the bonus round has no effect on the amount won. In other words, your choices don't determine which progressive you win, only how long it takes to reveal three matching coins for the progressive that has already been chosen for you.

It's important to note that each progressive can be chosen by the program using the RNG at the initiation of the bonus round. After the machine has randomly chosen the bonus you will win and you are picking coins, only one progressive can be won. So, you can win any of the progressives each time you get to the bonus, but the progressive you win is determined by a poll to the RNG, not the coins you pick.

If you don't like the way this machine operates, you can write to your local gaming commission. I think the bonus round is misleading, but regulators tend to be more lenient with bonus rounds because players are not making an additional bet and players can't lose.

You can also do a search in my columns on this site to see other questions and answers about 88 Fortunes.


John Robison

John Robison is an expert on slot machines and how to play them. John is a slot and video poker columnist and has written for many of gaming’s leading publications. He holds a master's degree in computer science from the prestigious Stevens Institute of Technology.

You may hear John give his slot and video poker tips live on The Good Times Show, hosted by Rudi Schiffer and Mike Schiffer, which is broadcast from Memphis on KXIQ 1180AM Friday afternoon from from 2PM to 5PM Central Time. John is on the show from 4:30 to 5. You can listen to archives of the show on the web anytime.

Books by John Robison:

The Slot Expert's Guide to Playing Slots
John Robison
John Robison is an expert on slot machines and how to play them. John is a slot and video poker columnist and has written for many of gaming’s leading publications. He holds a master's degree in computer science from the prestigious Stevens Institute of Technology.

You may hear John give his slot and video poker tips live on The Good Times Show, hosted by Rudi Schiffer and Mike Schiffer, which is broadcast from Memphis on KXIQ 1180AM Friday afternoon from from 2PM to 5PM Central Time. John is on the show from 4:30 to 5. You can listen to archives of the show on the web anytime.

Books by John Robison:

The Slot Expert's Guide to Playing Slots