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A coin lands heads with probability 1/4. What is the expected number of flips needed to see three heads?

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You flip a fair coin three times. What's the expected number of heads?A coin picked at random from one with P(heads) = 2/3 and one with P(heads) = 1/3 shows three heads in three flips. What is the probability the next flip is heads?What is the probability of an even number of heads when tossing 4 coins? 100 coins?

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