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Squarepoint·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

Quant interview at Squarepoint with a probability question that looks straightforward but has a few ways to go about it. Short and focused.

Questions Asked (1)

Q1

You roll a fair 6-sided die three times. What is the probability that the three outcomes are strictly increasing?

Algorithms & Data Structures
Author's notes

I started by counting total outcomes (6^3 = 216) then tried to count strictly increasing triples.

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AI HintsAI Generated

Suggested Approach

Recognize that the three rolls are independent and each outcome is equally likely. Count the number of strictly increasing sequences of length 3 from {1,2,3,4,5,6} and divide by the total number of possible outcomes (6^3 = 216).

Pro tip: Mention that the probability is equivalent to choosing 3 distinct numbers from 6 and then arranging them in increasing order, which simplifies to C(6,3)/6^3. This shows you can reframe the problem elegantly.

1. Understand the problem

Clarify that we roll a fair 6-sided die three times and want the probability that the outcomes are strictly increasing (e.g., 2,4,5).

2. Determine total outcomes

Calculate the total number of possible outcomes for three rolls: 6^3 = 216, since each roll is independent and has 6 possibilities.

3. Count favorable outcomes

Count the number of strictly increasing sequences of length 3 from the set {1,2,3,4,5,6}. This is equivalent to choosing 3 distinct numbers from 6, which can be done in C(6,3) = 20 ways.

4. Compute probability

Divide the number of favorable outcomes by the total outcomes: 20/216 = 5/54.

5. Verify and present

Double-check the counting logic and simplify the fraction. Present the final answer clearly.

Key Points to Mention

  • Independence of die rolls
  • Total outcomes = 6^3 = 216
  • Strictly increasing means all three outcomes are distinct and ordered
  • Number of increasing sequences equals number of 3-element subsets of {1,2,3,4,5,6}
  • Combination formula: C(6,3) = 20
  • Final probability = 20/216 = 5/54

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