Probability Paradoxes & Puzzles Calculators

Explore famous probability problems where the correct answer contradicts first intuition.

8 calculators in this category.

Probability paradoxes are problems where a natural first answer turns out to be wrong. They are useful because each one exposes a specific reasoning trap, such as ignoring how information was obtained or treating unequal cases as equally likely.

The tools in this category let you change the parameters of a classic puzzle and see how the result responds, which is usually the fastest way to understand why the surprising answer is correct.

Key concepts

Conditioning on information
Many paradoxes hinge on what a person knows and how they came to know it. The same event can have different probabilities depending on the process that revealed it.
Equally likely outcomes
Counting outcomes only works when each outcome has the same probability. Several classic puzzles go wrong by treating unequal cases as equal.
Base rates
The overall frequency of a condition in a population. Ignoring it is the source of the false positive paradox.