Type I and type II errors in an A/B test
Your team A/B tests a new order-execution algorithm against the current one, hoping it lowers trading costs. You run a hypothesis test on the measured cost difference.
State the null, define the type I and type II errors in this setting, describe their costs, and explain how they trade off.
Your answer
This one is open-ended. Work it through, then check your reasoning against the full solution.