Conditioning, expectation recurrences, and Bayes-first reasoning.
1. Biased Coin to Fair Bit (Von Neumann) [Medium]
2. Expected Tosses Until First HH [Medium]
3. Two Children, At Least One Boy [Easy]
4. Monty Hall Switching Odds [Medium]
5. Birthday Collision Threshold [Medium]
6. Bayes on Failing Test Alerts [Hard]Work each puzzle before reading the solution: predict the exact output or answer, name the rule that governs it, then check yourself.