SIG (Susquehanna)·Data Scientist·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

A brain teaser style math problem from a SIG Data Scientist interview. Short and self-contained but the kind of thing that trips you up if you rush the setup.

Questions Asked (1)

A barn contains spiders, chickens, and cows. Spiders have 8 legs, chickens have 2, and cows have 4. The total leg count is 520. The number of chickens is twice the number of cows, and the number of spiders is twice the number of chickens. How many chickens are there?

Algorithms & Data Structures

Author's notes

I set up the variable for cows as x, then chickens = 2x, spiders = 4x.

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AI HintsAI Generated

Suggested Approach

Translate the word problem into a system of linear equations by defining variables for each animal, then use substitution to reduce to a single variable equation. Solve for the number of cows first, then compute chickens using the given relationship.

Pro tip: After solving, verify your answer by plugging the numbers back into the original conditions to ensure consistency and catch arithmetic mistakes.

1. Define Variables

Let S = number of spiders, C = number of chickens, and W = number of cows. Clearly state what each variable represents.

2. Set Up Equations

Write the total leg equation: 8S + 2C + 4W = 520. Also write the given relationships: C = 2W and S = 2C.

3. Substitute and Simplify

Express all variables in terms of W using the relationships: C = 2W, S = 2C = 4W. Substitute into the leg equation to get 8(4W) + 2(2W) + 4W = 520.

4. Solve for W

Simplify the equation: 32W + 4W + 4W = 40W = 520, so W = 13. Then compute C = 2W = 26.

5. Verify and Answer

Check: S = 4W = 52, C = 26, W = 13. Total legs = 8*52 + 2*26 + 4*13 = 416 + 52 + 52 = 520. The number of chickens is 26.

Key Points to Mention

Translating verbal relationships into algebraic equations.
Using substitution to reduce a multi-variable system to one variable.
Maintaining clear variable definitions to avoid confusion.
Performing a sanity check by plugging values back into the original problem.
Communicating each step logically, as if explaining to a colleague.
Noting that the problem is a system of linear equations, a common data science modeling technique.

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