Mean and variance of the wait for heads
Question
A fair coin is flipped until the first head shows up. Let count all flips including that head. Find and .
Short answer
Mean , variance . is geometric with , so and .
Adapted from Joshi, Denson & Downes, Quant Job Interview Questions and Answers, Q3.6, p.81; question and answer rewritten by SelfMadeQuant.com.
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- Random Variables and Probability Mass Functions
- Derivation — Means and Variances of the Named Distributions
- Covariance and Correlation
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