Play the Monty Hall game.
You have three face down (gray) cards. The objective of the game is to guess which of the cards is the green card. Flow of the game:
1. First you pick a card.
2. A non-selected losing (red) card is turned face up. You now have the option to stick with your initial selection or to switch to the other face down (gray) card.
3. All the cards are turned face up. If you picked the green card you have won!
It is counter-intuitive but it has been mathematically proven that when you switch the probability to guess is twice than when you stick with your initial selection.
The app keeps the stats of your played games so you can verify if the reality conforms with the above statement.
For more details about the Monty Hall problem see https://en.wikipedia.org/wiki/Monty_Hall_problem.