Reason About Coffee-Quality Comparison Probabilities

Quick Overview

Analyze coffee-quality comparison probabilities by defining the event, independence, and ties, then use labeled orderings to derive conditional results.

Reason About Coffee-Quality Comparison Probabilities

Company: Mercor

Role: Software Engineer

Category: Statistics & Math

Difficulty: medium

Interview Round: Technical Screen

Two coffee shops, A and B, have the same distribution of coffee quality. Four purchased cups are labeled `A1`, `A2`, `B1`, and `B2`. What is the probability that the A cups are better than the B cups? Clarify the comparison event, dependence between purchases, and possible ties before giving a number. Explain what can be concluded from the stated information alone, then show the calculation under any additional assumptions you explicitly choose. The discussion also suggests using a sorting idea from an earlier request for a “slowest sorting algorithm.” Explain how ordering the four qualities can help with the probability calculation and what that sorting request leaves undefined. Do not assume a particular sorting algorithm was specified. ### What a Strong Answer Covers - The distinction between identical marginal distributions and independent sampling. - Whether both A cups must exceed both B cups or only their correspondingly labeled B cups. - A correct ranking/counting argument under stated assumptions, with explicit treatment of ties. - Why an algorithm's runtime does not determine the probabilities of the input orderings. ### Follow-up Questions - Can the four cups have identical quality distributions while the requested probability differs between sampling models? - How does a discrete quality scale change a strict-comparison calculation?

Overview: Analyze coffee-quality comparison probabilities by defining the event, independence, and ties, then use labeled orderings to derive conditional results.

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Mercor
Sep 3, 2026
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Two coffee shops, A and B, have the same distribution of coffee quality. Four purchased cups are labeled A1, A2, B1, and B2. What is the probability that the A cups are better than the B cups?

Clarify the comparison event, dependence between purchases, and possible ties before giving a number. Explain what can be concluded from the stated information alone, then show the calculation under any additional assumptions you explicitly choose.

The discussion also suggests using a sorting idea from an earlier request for a “slowest sorting algorithm.” Explain how ordering the four qualities can help with the probability calculation and what that sorting request leaves undefined. Do not assume a particular sorting algorithm was specified.

What a Strong Answer Covers Guidance

  • The distinction between identical marginal distributions and independent sampling.
  • Whether both A cups must exceed both B cups or only their correspondingly labeled B cups.
  • A correct ranking/counting argument under stated assumptions, with explicit treatment of ties.
  • Why an algorithm's runtime does not determine the probabilities of the input orderings.

Follow-up Questions Guidance

  • Can the four cups have identical quality distributions while the requested probability differs between sampling models?
  • How does a discrete quality scale change a strict-comparison calculation?
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