What to learn
Start with sample spaces, independence, mutually exclusive events and complements. Then add conditional probability, Bayes, counting-based probability and common distributions.
Practice order: concept, one worked example, guided question, fresh normal variants, then a mastery question under time pressure.
The interview method
Before calculating, define the event and decide whether direct counting or the complement is cleaner. State independence only when it actually holds. For Bayes questions, write the base rate before the signal accuracy.
Common traps
- Adding overlapping probabilities without subtracting the intersection.
- Treating draws without replacement as independent.
- Ignoring the base rate in a positive-signal problem.
- Using ordered outcomes in the numerator and unordered outcomes in the denominator.
Turn the method into evidence.
QuantPrep generates fresh probability variants and records speed, accuracy, difficulty and recency.
Train probability