alleryStart learning →An email user receives 147 emails per day on average, so X ~ P(147). What is the standard deviation of the number of emails received in a day?
AAbout 147.00
BAbout 12.12
CAbout 21609.00
DAbout 1.21
Answer & Solution
Correct answer: B. About 12.12
1. For a Poisson variable, the standard deviation is sqrt(μ).
2. Here μ = 147, so σ = sqrt(147).
3. sqrt(147) ≈ 12.1244, which rounds to about 12.12.
4. Option A repeats the mean rather than taking its square root, and option C squares μ instead.
_Source: OpenStax Introductory Statistics (CC BY 4.0), Ch 4 "Discrete Random Variables", section 4.6 Poisson Distribution_
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