Bayes Mental Math Drills
Bayes mental math drills for base rates, likelihoods, count tables, posterior approximations, and conditional probability interviews.
Candidates who understand Bayes but make arithmetic mistakes.
Use counts instead of formulas
Bayes arithmetic is often cleaner with a population of 1,000 or 10,000. Counts make base rates and false positives visible.
Separate likelihood from posterior
The probability of a signal given the state is not the probability of the state given the signal. The drill should force you to name both.
Concrete example
If 1 percent have a trait and a test catches 90 percent of true cases with 10 percent false positives, use 10,000 people to count true and false positives.
Approximate the posterior
After counting favorable signal cases and total signal cases, divide only at the end. Approximate if the prompt does not need a precise decimal.
Common mistakes
Candidates often ignore the base rate when the test sounds accurate. Base-rate arithmetic is the whole point of many Bayes prompts.
Practice the pattern
Use the LeetQuidity curriculum and calibration to turn this topic into a focused practice plan.