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Lyft·Data Scientist·Technical Phone Screen·Intermediate

Intermediate
Jul 2026

Summary

Lyft data science interview with a probability/stats question built around a pricing experiment scenario. The setup was clever and required more careful modeling than it first appeared.

Questions Asked (1)

Q1

In a pricing experiment, each new rider is offered two rides on their first day, where each ride is priced reasonably with some independent probability P. What is the probability that the rider takes exactly one ride the following day? What is the probability they become a permanent rider who rides every day going forward?

A/B Testing & ExperimentationProduct Analytics & MetricsPricing & Monetization
Author's notes

I stared at this for a second because the 'permanent rider' part felt open-ended.

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AI HintsAI Generated

Suggested Approach

Clarify the assumptions about the experiment: each ride is offered independently with probability P, and the rider's decision to take a ride is also independent with probability P. Then model the number of rides taken on the first day as a Binomial(2, P) distribution, and compute the probability of exactly one ride. For the probability of becoming a permanent rider, recognize that this requires taking both rides on the first day (probability P^2), and then assume that if they take both, they will continue riding every day thereafter.

Pro tip: Always state your assumptions explicitly and note that in reality, rider behavior is likely correlated (e.g., if they like the first ride, they may be more likely to take the second). This shows you understand the limitations of the model and can think critically about experiment design.

1. Clarify assumptions and define variables

Confirm that each ride is offered independently with probability P, and that the rider's decision to take each ride is also independent with probability P. Define X as the number of rides taken on the first day.

2. Model the number of rides on the first day

Since there are two rides, X follows a Binomial(2, P) distribution. The probability of exactly one ride is P(X=1) = 2P(1-P).

3. Determine the condition for becoming a permanent rider

A permanent rider is defined as someone who rides every day going forward. This requires taking both rides on the first day (X=2), with probability P^2. Assume that if they take both, they become permanent with probability 1.

4. Compute the required probabilities

The probability of exactly one ride is 2P(1-P). The probability of becoming a permanent rider is P^2.

5. Discuss implications and limitations

Mention that this is a simplified model and that in practice, probabilities may not be independent, and the definition of 'permanent' may require additional conditions.

Key Points to Mention

  • Binomial distribution for independent trials
  • Independence assumption for ride offers and rider decisions
  • Probability of exactly one success in two trials: 2P(1-P)
  • Probability of two successes: P^2
  • Definition of a permanent rider and the assumption that taking both rides leads to permanent status
  • Limitations: real-world behavior may be correlated, and P may vary across riders

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