Estimation question – Google product manager interview (Time spent at stop lights)

Click to expand the mind map for a detailed view.

Mindmap: Google Product Manager Mock Interview – Estimating Time Spent at Stoplights

1. Introduction

  • Interviewer: Akshat, former PM at Google (Android Messages, Google Stadia).
  • Candidate: Anika, former PM at Google (Search, YouTube Ads).
  • Objective: Demonstrate how to ace a PM interview by estimating the total time drivers in the U.S. spend at stoplights annually.

2. Clarifying Questions

  • Question 1: Is this question specific to a region or global?
  • Answer: Focus on the United States.
  • Question 2: Who is included in “average person”?
  • Answer: Drivers (people behind the steering wheel).
  • Question 3: Pre- or post-COVID data?
  • Answer: Pre-COVID world.

3. High-Level Approach

  • Equation: Total time = (Number of drivers) × (Time spent at stoplights per driver annually).
  • Segmentation: Break down drivers into three groups:
  1. Commuters: Daily drivers to/from work.
  2. Transport Drivers: People who drive for their job (e.g., freight, delivery, taxi drivers).
  3. Leisure Drivers: Occasional drivers (e.g., errands, weekend trips).

4. Detailed Breakdown by Driver Segment

4.1 Commuters

  • Daily Driving Time: ~2 hours/day (1 hour each way).
  • Time at Stoplights: ~15% of driving time (10 minutes per hour).
  • Days Driven Annually: ~200 days (5 days/week × 52 weeks, rounded down).
  • Calculation: 2 hours/day × 200 days × 15% = 80 hours/year.

4.2 Transport Drivers

  • Daily Driving Time: ~8 hours/day (full workday).
  • Time at Stoplights: ~10% of driving time (less peak traffic).
  • Days Driven Annually: ~300 days (includes weekends).
  • Calculation: 8 hours/day × 300 days × 10% = 240 hours/year.

4.3 Leisure Drivers

  • Daily Driving Time: ~2.5 hours/day (errands, weekend trips).
  • Time at Stoplights: ~10% of driving time (less peak traffic).
  • Days Driven Annually: ~100 days (2 days/week × 52 weeks, rounded down).
  • Calculation: 2.5 hours/day × 100 days × 10% = 25 hours/year.

5. Estimating Number of Drivers

5.1 Commuters

  • Total Working Adults in U.S.: ~150 million.
  • Percentage Commuting: ~80%.
  • Number of Commuters: 150M × 80% = 120 million.

5.2 Transport Drivers

  • Percentage of Working Adults: ~7% (10 million).
  • Number of Transport Drivers: 10 million.

5.3 Leisure Drivers

  • Total U.S. Population: ~300 million.
  • Eligible Drivers (16+ years): ~200 million.
  • Number of Leisure Drivers: 200 million.

6. Aggregating Total Time Spent at Stoplights

  • Commuters: 120M × 80 hours = 9,600 million hours.
  • Transport Drivers: 10M × 240 hours = 2,400 million hours.
  • Leisure Drivers: 200M × 25 hours = 5,000 million hours.
  • Total Time: 9,600 + 2,400 + 5,000 = 17 billion hours/year.

7. Refining the Analysis

  • Areas for Improvement:
  1. Driver Segmentation: Further divide groups (e.g., short vs. long commutes, urban vs. rural transport drivers).
  2. Stoplight Variability: Account for differences in stoplight durations (e.g., urban vs. suburban intersections).
  • Next Steps:
  • Gather more granular data on driver habits and stoplight behavior.
  • Adjust estimates based on sub-segment variations.

8. Conclusion

  • Key Takeaway: The final number (17 billion hours) is less important than the structured, logical approach to solving the problem.
  • Interviewer Feedback: Anika excelled in structuring her response, explaining her thinking, and managing time effectively.
  • Call to Action: For more interview prep, visit IGotAnOffer.

Related Posts