Math Questions at Coupang: What to Expect

Math questions appear in roughly 10% of Coupang's technical interview problems. While this may seem low, these problems are critical filters. Coupang's core operations—supply chain logistics, inventory optimization, dynamic pricing, and recommendation algorithms—are built on mathematical models. Your ability to reason through these problems demonstrates you can handle the quantitative thinking required to scale one of Asia's largest e-commerce platforms.

What to Expect — Types of Problems

Coupang's math questions typically fall into three categories:

1. Probability & Statistics: Expect problems involving combinatorics, expected value, or conditional probability. These test your understanding of random processes, relevant to A/B testing or fraud detection systems.
2. Modular Arithmetic & Number Theory: Problems involving properties of numbers, remainders, or divisibility. These are common in problems related to hashing, distributed systems, or generating unique identifiers.
3. Simple Mathematical Modeling: Word problems that require you to translate a real-world scenario (e.g., warehouse packing, delivery routing) into a concise mathematical formula or algorithm. The math itself is often not advanced, but the modeling step is key.

You will not encounter advanced calculus or linear algebra. The focus is on applied, discrete mathematics that can be translated into efficient code.

How to Prepare — Study Tips with One Code Example

Focus your preparation on core concepts. Review probability rules (especially for independent and dependent events), combinatorics (permutations and combinations), and modular arithmetic properties (like (a * b) % m = ((a % m) * (b % m)) % m). Practice translating word problems into clean code.

A frequent pattern is using the GCD (Greatest Common Divisor) to simplify problems involving ratios, cycles, or divisibility. Here is a common implementation of the Euclidean algorithm to compute GCD, a fundamental tool for such problems.

def gcd(a, b):
    while b:
        a, b = b, a % b
    return a

# Example: Simplify a ratio of items
def simplify_ratio(num, den):
    divisor = gcd(num, den)
    return num // divisor, den // divisor

Recommended Practice Order

1. Master Fundamentals: Ensure you can implement GCD, LCM, factorial, and n-choose-k calculations from memory.
2. Solve Probability Drills: Work on classic problems involving dice, cards, and balls in urns to build intuition.
3. Tackle Modular Arithmetic: Practice problems involving cyclic patterns and remainders.
4. Simulate Scenarios: For complex probability questions, write quick simulation code to verify your analytical answer.
5. Do Timed Practice: Finally, solve Coupang-specific problems under interview constraints to build speed and confidence.

Practice Math at Coupang