Brain Teasers & Mental Math
Probability: you roll a fair die repeatedly. What is the expected number of rolls to see your first 6?
Model answer
6 rolls.
This is geometric with p = 1/6, so the expected number of trials to the first success is 1/p = 6.
Self-consistent argument: let E = expected rolls. Each roll, with probability 1/6 you get…
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