SLOT MACHINES! They are designed to make money, they can be set to different percentage pay-outs and if you get a bad Casino setting the lowest possible percentage win rate you have no chance.
My Wife was a Manageress in a Slot machine arcade and even she had no access to alter the Percentage Rate, that was set by the mechanic's who came around on a weekly visit to empty them and set the rate depending on how much the machine had taken the previous week, but even set at a high percentage pay out does not mean you will get a set amount back for every £100 put into it, they don't work like that, the rate is set over the Lifetime of the machine which could be weeks, months or even years depending on it's popularity.
She had some machines that were never changed in the Arcade because they were so Popular, she had others that could be changed every 6 or 12 months depending on their popularity,
There are ways to beat them, but even knowing all the secrets you can still lose, I once saw one guy put in over £60 in one machine and every time he got 3 nudges he held the two symbols that matched, and spun the reels and not once did he get a win. I wanted to tell him what he was doing wrong, but couldn't as It could have cost her job, but after he left I put £2 in the machine and walked away with £50 in 10 minutes.
Not all machines work this way but they want you to hold after a nudge, some will automatically hold for you after a nudge, if you do usually you will lose, the one tip I will give you is if you find the right machine's, NEVER Hold after a nudge, Cancel it and it will always spin to a win, not the one you would have made by holding matching symbols, but a win never the less.