Math Questions at Grammarly: What to Expect

Math questions appear in roughly 25% of Grammarly's technical interview problems. They aren't about advanced calculus; they test your ability to translate logical rules, constraints, and relationships into efficient code. Grammarly's product—analyzing text for clarity and correctness—is built on pattern recognition, probability, and rule-based systems. Solving these problems demonstrates you can think algorithmically about the underlying structures that power grammar checking, plagiarism detection, or readability scoring.

What to Expect — types of problems

Grammarly's math-focused questions typically fall into two categories. First, combinatorics and probability: problems involving counting arrangements, calculating odds, or simulating scenarios. You might be asked to compute the number of ways to correct a sentence given certain grammar rules or estimate the likelihood of a specific writing pattern.

Second, modular arithmetic and number theory: these problems involve remainders, divisibility, or cyclic patterns. They often appear in questions related to hashing, distributing workloads, or handling repeating sequences—concepts relevant to building scalable text-processing pipelines.

Expect constraints that require an O(1) mathematical solution rather than a brute-force simulation. The interviewer will look for your ability to identify the formula or property that bypasses unnecessary computation.

How to Prepare — study tips with one code example

Focus on the fundamentals. Review modular arithmetic, basic combinatorics (permutations, combinations), and probability rules. Practice deriving formulas before coding. Always walk through small examples to validate your logic.

A common pattern is using the GCD (Greatest Common Divisor) or modulo operation to reduce a problem to its periodic core. For example, many "count divisible numbers in a range" problems have an O(1) mathematical solution instead of a linear loop.

def count_divisible(A, B, K):
    """Count numbers divisible by K in range [A, B] inclusive."""
    # Adjust A to the first divisible number in range
    if A % K != 0:
        A += K - (A % K)
    if A > B:
        return 0
    return (B - A) // K + 1

This approach runs in O(1) time by calculating the count directly, instead of O(n) from looping. Spotting this optimization is key.

Recommended Practice Order

1. Core Concepts: Start with basic problems involving modulo, divisibility, and simple counting on platforms like LeetCode (e.g., "Count Primes," "Happy Number").
2. Combinatorics: Practice problems that require calculating permutations or combinations, often using factorial computations with modular inverses for large numbers.
3. Probability: Tackle simulation problems where you can first brute-force for small cases to find a pattern, then derive the closed-form expression.
4. Grammarly-Specific: Finally, work on problems tagged with "Grammarly" to familiarize yourself with their problem style and constraints.

Consistently ask yourself: "Can I replace this loop with a formula?"

Practice Math at Grammarly