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Capital One·Data Scientist·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

Capital One Data Scientist interview with a pretty involved quantitative case study about a billing bug and its profit impact. The problem looked like a finance/analytics hybrid and required careful cohort-level accounting across three months.

Questions Asked (1)

Q1

A registration bug affects Premium users for three months. Cancelled Premium users stay registered (earning 2% commission and incurring $1.25/month admin cost) and new Premium users go unregistered (earning only 1% commission, no admin cost). With 400 cancellations and 2,000 new Premium users each month, and given average spending figures, compute the total net profit impact versus correct functioning, broken down by cohort and line item.

Product Analytics & MetricsPricing & MonetizationRoot Cause Analysis
Author's notes

This one took me a while to even parse correctly.

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AI HintsAI Generated

Suggested Approach

First, clarify the baseline (correct functioning) and the buggy state for each cohort, then compute the monthly and cumulative profit impact over three months. Break down the impact by cohort (cancelled Premium users and new Premium users) and by line item (commission and admin cost), ensuring consistent units and time periods.

Pro tip: Always state your assumptions explicitly (e.g., average spending, commission rates) and consider whether the bug affects revenue or cost, and whether the impact compounds monthly. This shows rigor and prevents miscommunication.

1. Define baseline and buggy scenarios

Establish what 'correct functioning' means for each cohort: cancelled users should be unregistered (no commission, no admin cost), new users should be registered (2% commission, $1.25/month admin cost). In the buggy state, cancelled users remain registered (2% commission, $1.25/month admin cost) and new users are unregistered (1% commission, no admin cost).

2. Compute monthly impact per cohort

For each cohort, calculate the difference in commission and admin cost between buggy and correct states. For cancelled users: buggy has 2% commission and $1.25 admin cost, correct has 0% and $0. For new users: buggy has 1% commission and $0 admin cost, correct has 2% commission and $1.25 admin cost.

3. Aggregate over three months

Multiply the monthly impact per cohort by 3 to get the total impact over the three-month period. Sum the impacts across cohorts to get the overall net profit impact.

4. Present breakdown by cohort and line item

Organize the results in a table or structured format showing the impact for each cohort (cancelled, new) and each line item (commission, admin cost), with monthly and total figures. Clearly state whether each impact is positive or negative for profit.

Key Points to Mention

  • Clarify the baseline: correct functioning means cancelled users are unregistered and new users are registered with 2% commission and $1.25/month admin cost.
  • For cancelled users, the bug causes extra commission (2% of spending) and admin cost ($1.25/month) per user, which are losses.
  • For new users, the bug causes lost commission (1% instead of 2%) but saves admin cost ($1.25/month), so net impact depends on average spending.
  • Calculate monthly impact per cohort: cancelled users: 400 * (0.02 * avg_spend + 1.25); new users: 2000 * (0.01 * avg_spend - 1.25).
  • Multiply monthly impacts by 3 to get total three-month impact, and sum for overall net profit impact.
  • Express results in dollars and clearly label positive/negative impacts on profit.

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