Hi Adrian,
The app is great! Unfortunately, some questions are quite hard (the "Getting serious" category) and there are no solutions.
I found this: https://kalamdeveloper.wordpress.com/2017/12/18/games-mathematicsprobability-puzzles-getting-serious-33-33-solved-33/
But not all have proper explanation. Would it be an idea to extend their solutions with more text/visualisations?
Best