Problem-Solving and Data AnalysisVery hardExactly two heads in three flips
Problem-Solving and Data Analysis practice question
A fair coin is flipped three times. What is the probability of getting exactly two heads?
Answer: 3/8 or 0.375
There are 2³ = 8 equally likely sequences. Exactly two heads happens in three of them: HHT, HTH, THH. Probability: 3/8.
Common wrong answers
- If you answered 1/8
- 1/8 is the probability of one specific sequence, such as HHT; there are three sequences with exactly two heads.
- If you answered 1/2
- 1/2 is the probability of AT LEAST two heads (HHT, HTH, THH, HHH).
- If you answered 2/3
- 2/3 is 'two out of three' misread as a probability; the outcomes are the 8 sequences.
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