Waiting to see both faces
You flip a fair coin repeatedly and stop as soon as you have seen both a head and a tail at least once. What is the expected number of flips? (to 2 decimals)
Show hints (2)+
- The first flip always reveals one face for free; only the second face requires waiting.
- Waiting for a face with probability 1/2 has expectation 1/(1/2) = 2.
Answer
Reveal answer →Final answer
3 (± 0.01)
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