You are being to simplistic.
Of course you can work out the theoretical EV based on 5% edge, the same as you would with say 0.5% blackjack.
But the variance of slots is massive compared to cards or even roulette & the chances of getting even remotely close to 5% during this
WR are pretty much zilch.
The probability is your return will be much less than 95% and you will bust out. But you only need one or two decent hits and it will be a totally different story...
I know; I've been there, done that - many times!
Bookmarks