Probability Puzzles That Break Your Brain

Probability Puzzles That Break Your Brain

Odds, dice and coin flips. Your gut will lie to you on these.

10 questions · scored on right answers

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What's in this test (10 questions)
  1. How many people need to be in a room for a 50% chance that two share a birthday?
  2. Game show: 3 doors, a car behind one. You pick Door 1. The host, who knows, opens Door 3 to show a goat. Should you switch to Door 2?
  3. A fair coin lands heads 5 times in a row. What are the odds the next flip is heads?
  4. You roll two dice. Which total is most likely?
  5. Flip a coin 6 times. Which exact sequence is more likely: HHHHHH or HTHTTH?
  6. A disease affects 1 in 1,000 people. A test is 99% accurate. You test positive. Roughly what's the chance you have it?
  7. Linda is 31, outspoken, and was a philosophy major who protested for social justice. Which is more likely?
  8. Lottery: which is more likely to win — 1, 2, 3, 4, 5, 6 or a random mix of numbers?
  9. You flip 2 fair coins. What's the chance of getting exactly one heads?
  10. Among all two-child families with at least one boy, what fraction have two boys?