Which bag?

Balls come out of a hidden bag. How likely is it bag A? As many as you can in 60 seconds, each one scored the moment you answer.

How it works

1. Each round shows two bags, how one was picked, and the balls drawn from it. Slide to how likely it's bag A.
2. You score how close you are to the exact chance, measured in odds: 10, 5 or 2 points. The real bag doesn't count.
3. Rounds get harder as you improve: uneven priors, lopsided bags, balls not put back, rare bags.

It trains updating beliefs on evidence (Bayes). After every round you see the best answer and why.

Play which bag?

Play with friends or a club

Challenge a friend with a duel link, or run a tournament for a club or class: one link, the same rounds for everyone, one run each, and a live leaderboard.

Also try Balloon, or the probability puzzles.