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.
Reason About Coffee-Quality Comparison Probabilities
Mercor
Sep 3, 2026
mediumSoftware EngineerTechnical ScreenStatistics & Math
5
0
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?