Odds Oracle
Sixteen questions about cards, dice, coins, wheels and birthdays. Commit to a number before you see the answer — estimating probabilities is a skill, and the only way to know whether you have it is to be scored. Every answer comes with the combinatorics it falls out of.
Your answers
Scoring
Within 1 percentage point is sharp, within 5 is close, within 15 is off, and beyond that is way off. Mean error is the average absolute distance across every question you've answered — the single number worth watching.
Most people are badly calibrated in one specific direction: they overestimate rare events and underestimate compound ones. Four rolls of a die feel like they should produce a six more often than 52% of the time; twenty-three people feel like far too few for a shared birthday. Both intuitions are wrong, and the derivations show why.