Sig·Software Engineer·Technical Phone Screen·Junior

Junior

Apr 2026

Summary

SIG quant engineer interview threw a classic brain teaser at me, the kind where you set up a system of equations and just grind through it. Pretty standard for a quant screen.

Questions Asked (1)

Chickens, cows, and spiders share a cage with a total of 560 legs. The number of chickens is twice the number of cows, and the number of spiders is twice the number of chickens. How many spiders are there?

Algorithms & Data Structures

Author's notes

Set up three variables and the leg count equation.

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AI HintsAI Generated

Suggested Approach

Translate the word problem into algebraic equations by assigning variables to the number of each animal, then use the given relationships to express all variables in terms of one. Solve the resulting linear equation for the total number of legs, and verify the solution by checking the total leg count.

Pro tip: After solving, always plug the numbers back into the original problem to ensure the total legs match and the ratios are correct; this catches careless errors and shows attention to detail.

1. Define variables

Let C be the number of chickens, W be the number of cows, and S be the number of spiders.

2. Translate relationships

Write equations based on the problem: C = 2W and S = 2C. Also, note the number of legs per animal: chickens have 2, cows have 4, spiders have 8.

3. Express in one variable

Substitute C = 2W into S = 2C to get S = 4W. Then express total legs in terms of W: 2C + 4W + 8S = 560.

4. Solve the equation

Substitute C and S in terms of W: 2(2W) + 4W + 8(4W) = 560. Simplify and solve for W, then find S.

5. Verify and answer

Check that the total legs equal 560 and that the ratios hold. State the final number of spiders clearly.

Key Points to Mention

Assign variables clearly and define what each represents.
Use the given ratios to express all quantities in terms of a single variable.
Account for the correct number of legs per animal (chickens: 2, cows: 4, spiders: 8).
Set up and solve the linear equation for total legs.
Verify the solution by substituting back into the original conditions.
Communicate the steps logically, as if explaining to a teammate.

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