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Consecutive Heads vs Tails

Hard · Probability & Statistics · Quant Trader interview question · probability, expected-value, markov-chain, mental-math

You are flipping a fair coin. What is the difference between the expected number of flips required to observe the sequence "Heads-Heads" (HH) versus the expected number of flips required to observe the sequence "Tails-Heads" (TH)?