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Sig·Software Engineer·Technical Phone Screen·Junior

Junior
Apr 2026

Summary

SIG quant researcher screen, basically just a math puzzle about counting legs in a barn. Short and painless but I second-guessed my algebra the whole time.

Questions Asked (1)

Q1

A barn has spiders (8 legs), chickens (2 legs), and cows (4 legs). Total legs add up to 520. Chickens are twice the number of cows, and spiders are twice the number of chickens. How many spiders are there?

Algorithms & Data Structures
Author's notes

Set up the variables fine, cows = x, chickens = 2x, spiders = 4x.

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AI HintsAI Generated

Suggested Approach

Translate the word problem into algebraic equations by assigning variables to each animal type, then use the given relationships to express all variables in terms of one variable. Solve the resulting equation for the base variable, then compute the number of spiders.

Pro tip: After solving, verify your answer by plugging the numbers back into the original problem to ensure all conditions are satisfied. This catches arithmetic errors and demonstrates thoroughness.

1. Define variables

Let S = number of spiders, C = number of chickens, and W = number of cows (use W to avoid confusion with C for chickens).

2. Express relationships

Translate the given relationships into equations: C = 2W (chickens are twice cows) and S = 2C (spiders are twice chickens).

3. Write leg-count equation

Set up the total legs equation: 8S + 2C + 4W = 520.

4. Substitute and solve

Substitute S and C in terms of W into the leg equation, simplify, and solve for W. Then find S = 4W.

5. Verify and answer

Check that the total legs match 520 and that all relationships hold, then state the number of spiders.

Key Points to Mention

  • Variable assignment and clear notation to avoid confusion (e.g., using W for cows instead of C).
  • Translating verbal relationships into algebraic equations.
  • Setting up the total legs equation with correct coefficients (8, 2, 4).
  • Substitution method to reduce to a single variable.
  • Solving the linear equation and computing the final answer.
  • Verification of the solution against all given conditions.

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