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Tips & Tricks for solving Fermi Questions

A Fermi question is a problem-solving question that requires estimation to arrive at a rough answer. Named after physicist Enrico Fermi, these questions typically involve making educated guesses and assumptions based on limited information.

A general good approach for solving Fermi Questions is to follow these steps:

  1. Break down the problem: Try to break the problem down into solvable questions.
  2. Make reasonable assumptions: Identify and state any assumptions you are making.
  3. Use approximations: Simplify the calculations by using rounded numbers where appropriate.
  4. Check your work: Verify if the answer makes sense and is plausible given the context.

When faced with a Fermi question in an interview and you have no clue about a certain assumption, follow these steps:

  1. Acknowledge the Uncertainty: Start by acknowledging that you are unsure about the assumption. This shows honesty and transparency.
    Example: "I'm not entirely sure about the exact value for this assumption, but I will make an educated guess."

  2. Use General Knowledge: Draw on any general knowledge you might have related to the topic to make a reasonable estimate.
    Example: "I know that the population of a large city can range from 1 to 10 million people, so I'll use 5 million as a middle-ground estimate."

  3. Explain Your Reasoning: Clearly explain the logic behind your guess. This demonstrates your problem-solving approach and how you handle uncertainty.
    Example: "Given that many major cities have populations in the range of a few million, I'll assume 5 million for simplicity, which seems reasonable for a large metropolitan area."

  4. Seek Feedback: If possible, ask the interviewer if the assumption seems reasonable. This can provide guidance and show that you are open to input.
    Example: "Does that assumption sound reasonable, or would you suggest a different approach?"

  5. Proceed with the Estimate: Use your assumption to continue solving the problem. Ensure that your subsequent calculations are logical and consistent with the assumption made.
    Example: "Based on the assumption of 5 million people, I'll calculate the proportion who might use a certain service..."

By following these steps, you demonstrate your ability to handle uncertainty effectively, think critically, and communicate clearly, all of which are valuable skills in any problem-solving scenario.

Your assumptions should be detailed enough to provide a logical basis for your estimates but not so detailed that they overcomplicate the problem. Strive for a balance that allows you to make reasonable approximations.

Interviewers are assessing your problem-solving abilities, logical reasoning, quantitative skills, ability to make and justify assumptions, and how you handle uncertainty.

  • Avoid overcomplicating the problem with unnecessary details.
  • Don't get stuck on finding the "perfect" assumption.
  • Ensure your assumptions are reasonable and explainable.