Compare Ad-Insertion Strategies: Expected Ads and Probabilities
Overview
This question evaluates understanding of probability theory, expected value calculation, and stochastic modeling as applied to ad-insertion strategies in sequential data.
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Jul 12, 2025, 6:59 PM
Data Scientist
Onsite
Statistics & Math
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Newsfeed Ad-Insertion Strategies
You are evaluating two ways to insert ads into a user's newsfeed. Assume a user views a contiguous sequence of posts.
Strategies
- Strategy A: Each post independently has a 4% chance (p = 0.04) of being an ad.
- Strategy B: Exactly one ad is randomly inserted in every block of 25 posts (non-overlapping blocks).
Questions
- Under Strategy A, what is the expected number of ads in 100 posts?
- Under Strategy B, what is the (expected) number of ads in 100 posts? Compare to Strategy A.
- Under Strategy A, what is the probability a user sees at least one ad in the next 25 posts?
Hint: Use linearity of expectation and binomial probabilities. P(at least one) = 1 − (1 − p)^n.
Solution
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