First tail within two flips

Each of 33 people repeatedly flips the same biased coin, which shows heads with probability p=0.25p = 0.25, stopping at their first tails. What is the probability that none of the three needs more than two flips?

Show hints (2)+
  1. One person needs >2>2 flips iff the first two are both heads: probability p2p^2.
  2. So one finishes in ≤2\le 2 with probability 1−p2=15/161-p^2 = 15/16. Cube for three independent people.

Answer

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0.824 (± 0.001)

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