Probability Interview Preparation: Find the Right Practice

Choose practice according to the mistake you are making. If you can calculate a conditional probability but use the wrong population, another formula sheet may not address the problem.

The Probability & Trading Interview Workbook is structured around defining an experiment, calculating within it and adapting when assumptions change.

A short diagnostic

A box is chosen fairly from two boxes. Box A contains one red and one blue token; box B contains three red and one blue. Draw uniformly within the chosen box. Is the red probability the same as pooling all six tokens?

No. Equal box selection gives 0.5 × 0.5 + 0.5 × 0.75 = 0.625. Pooling gives 4/6, approximately 0.667. The first procedure gives tokens in the smaller box more individual weight.

If you immediately pooled the tokens, the gap concerns the selection model. If you set up the two-stage calculation correctly but made a numerical slip, the repair is different. If you reached the answer but cannot explain the weighting, practice the spoken reasoning.

Match the workbook to the gap

The book covers conditioning, counting, indicators, expectation, dependence, finite waiting and stopping, introductory continuous probability, estimation and original toy decision games. Forty exercises include solutions, and two extended mocks introduce changed assumptions. An editable log helps record the first wrong step.

It does not cover every quant interview topic. Advanced stochastic calculus, full statistical theory, comprehensive coding preparation and firm-specific assessment claims are outside its scope.

Read the actual PDF preview before choosing the workbook. The preview includes complete lessons, not just a cover and contents page.

For free practice first, use base rates, indicators or stopping rules. Keep an error log so the next session follows the evidence.