This interview question evaluates statistical assumptions, formulas, estimation strategy, uncertainty, edge cases, and interpretation in a realistic interview setting. A strong answer for Model Feature Adoption Probability for Users states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.
##### Scenario
Feature adoption probability modeling
##### Question
Each user adopts the wallet feature with independent probability p. For n users:
(a) expected number of adopters,
(b) probability that at least one adopts,
(c) given that at least one adopts, probability exactly two adopt.
##### Hints
Use the binomial distribution, complement rule, and conditional probability.
Quick Answer: This interview question evaluates statistical assumptions, formulas, estimation strategy, uncertainty, edge cases, and interpretation in a realistic interview setting. A strong answer for Model Feature Adoption Probability for Users states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.
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Model Feature Adoption Probability for Users
Feature Adoption Probability Modeling
Context
You are analyzing adoption of a new wallet feature. Each of n users independently adopts the feature with identical probability p. Let X be the number of adopters among the n users.
Tasks
(a) Compute the expected number of adopters.
(b) Compute the probability that at least one user adopts.
(c) Given that at least one user adopts, compute the probability that exactly two users adopt.
Hints
Model X with a Binomial(n, p) distribution.
Use the complement rule for "at least one": P(X ≥ 1) = 1 − P(X = 0).
Use conditional probability: P(A | B) = P(A ∩ B) / P(B).
Clarifying Questions to Ask Guidance
Clarify the random variables, distributional assumptions, independence assumptions, and desired output.
Show enough derivation for the interviewer to follow the reasoning.
Explain how you would validate the result with simulation or sensitivity checks.
What a Strong Answer Covers Guidance
A correct setup with definitions, formulas, and boundary conditions.
A step-by-step derivation or estimation plan.
Interpretation of the result, including uncertainty and practical limitations.
Checks for assumptions, edge cases, and numerical stability.
Follow-up Questions Guidance
How would the result change if the assumptions were relaxed?
Can you verify the answer with a simulation?
What is the most likely source of estimation error?