Why you run an A/B test for whole weeks, not "until it's ready"
Your power calculation says you'll hit the required sample size in about 9 days. A colleague wants to stop exactly then. You argue for rounding up to a full 14 days.
Explain why experiments should run in whole-week multiples, and how day-of-week composition can bias a mid-cycle stop, separate from the sample-size question.
Your answer
This one is open-ended. Work it through, then check your reasoning against the full solution.