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IMC·Data Scientist·Technical Phone Screen·Intermediate

Intermediate
Jul 2026

Summary

IMC data scientist interview with a probability question that looks clean on the surface but requires you to actually set up the geometry carefully. One question, not a lot of fluff.

Questions Asked (1)

Q1

X and Y are independent uniform random variables on [0,1]. Let L be the larger of the two and S the smaller. What is P(L² > S)?

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

I stared at this for a bit because writing it in terms of max and min felt clunky.

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AI HintsAI Generated

Suggested Approach

Recognize that L and S are the order statistics of two independent uniform variables, so their joint density is constant (2) over the triangle 0 ≤ S ≤ L ≤ 1. Then compute the probability by integrating this joint density over the region where L² > S, i.e., S < L².

Pro tip: After solving, sanity-check your answer by considering extreme cases: if the condition were L > S (always true), probability should be 1; if L² > 1 (never true), probability should be 0. Also, note that the answer is a simple fraction, which is typical for uniform order statistic problems.

1. Identify the joint distribution

Since X and Y are independent uniform on [0,1], the joint density of (L, S) is f(l, s) = 2 for 0 ≤ s ≤ l ≤ 1, and 0 otherwise.

2. Define the region of interest

The event L² > S corresponds to the region in the (l, s) plane where s < l², within the triangle 0 ≤ s ≤ l ≤ 1.

3. Set up the integral

Compute P(L² > S) = ∫∫_{s < l²} 2 ds dl over the region. Determine the limits: for a given l, s ranges from 0 to min(l, l²). Since l² ≤ l for 0 ≤ l ≤ 1, the upper limit is l².

4. Evaluate the integral

Integrate with respect to s first: ∫_{0}^{1} ∫_{0}^{l²} 2 ds dl = ∫_{0}^{1} 2l² dl = 2/3.

5. Verify and interpret

Check that the result is between 0 and 1 and makes intuitive sense. Optionally, derive using order statistics or geometric probability for confirmation.

Key Points to Mention

  • Order statistics of independent uniform variables
  • Joint probability density function of (L, S)
  • Integration over the region defined by L² > S
  • Geometric interpretation: area in the unit square
  • Symmetry and independence of X and Y
  • Sanity checks for extreme cases

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.