Study guides
Read the idea, then answer a question
Each guide takes under ten minutes, links to the public sources it draws on, and ends with a free question.
01 · SQL screen · 8 min read
SQL window functions for top-N and dedupe questions
How to use ROW_NUMBER, RANK and DENSE_RANK with PARTITION BY to answer top-N per group and keep-latest-row questions in a live SQL screen.
02 · Experimentation · 9 min read
A/B test sample size, power and the peeking problem
How to size an experiment from baseline rate and minimum detectable effect, and why checking results early inflates false positives.
03 · Experimentation · 6 min read
Sample ratio mismatch: the check to run before reading any result
What a sample ratio mismatch is, how to test for it with a chi-squared check, and the usual root causes interviewers expect you to name.
04 · Analytics case · 7 min read
Reading retention curves and cohorts in a product case
How to define a retention event, read the shape of a curve, and compare signup cohorts so you can explain why retention moved.
05 · Analytics case · 8 min read
Evaluating AI agents: offline evals, pass@k and production metrics
How to talk about measuring an AI agent in an interview: task success, graders, pass@k versus pass^k, and the online metrics that confirm it.