Slot Machine probability

[Genesis]

Hello,

 

I'm trying to create a slot machine NPC, where players pay a fee to play. They have a x chance of winning y zeny. Does anyone have a snippet of a script illustrating a zeny slot machine's formula for making sure the house always wins?

 

 

As far as I can remember from my probability classes is the following formula:

 

EV = Chance_of_winning * (winnings - bet) + (chance of winning * -bet)

 

However, I'd like to be able to account for multiple instances of winning (not always the jackpot) but at the same time making sure the house always wins.

 

 

TLDR: I nneed a snippet of a zeny slot machine that shows the formula used to make sure the house wins, while ensuring the player gets SOME zeny back. 

[Genesis]

Bump, anyone have any ideas?