FastMath for Consulting Interview Preparation

What Is FastMath?

FastMath was created by Matthew Tambiah, a former McKinsey consultant with an MBA from MIT Sloan. His stated teaching approach emphasizes choosing a calculation method suited to the problem rather than applying the same procedure to every calculation. The resource translates that approach into instruction in numerical techniques and quantitative problem solving.

Although consulting interviews are an important application, FastMath also addresses business interviews and workplace calculations beyond consulting. Its curriculum connects arithmetic methods with practical business questions.

For directory purposes, it belongs in the self-study category. Candidates should evaluate it as a focused numerical resource and make separate plans for any application, networking, or interview needs outside that scope.

What Does FastMath Help Candidates Prepare For?

Mental Math and Large-Number Calculations

A recognizable part of the curriculum is No-Zero Multiplication and Division: methods for calculating with large numbers without writing out and counting every zero. Associated lessons address how to read, write, and express numerical magnitudes.

The broader material includes factoring and reordering calculations, working with common multiplication and division patterns, converting fractions to percentages or decimals, and calculating with percentages.

When assessing whether this material matches a preparation need, distinguish between choosing the right calculation and executing it. For example, identifying a revenue equation and carrying out its arithmetic are separate tasks; an error log can track them separately.

Business Calculations

Business applications include profitability, breakeven analysis, compound growth, compound annual growth rates, and introductory net present value calculations. This gives the curriculum a business context beyond isolated arithmetic exercises.

Candidates can prioritize topics according to their preparation needs. The course syllabus should not be treated as an employer’s official list of required interview knowledge.

Market Sizing and Estimation

FastMath includes market-sizing and estimation lessons, a market-sizing framework, and worked examples. This makes estimation a distinct study area within the curriculum rather than merely an incidental use of multiplication.

When applying this material, practice explaining the assumptions behind the estimate as well as calculating the result. State what is being counted, how the estimate is organized, and what the answer implies.

How FastMath Works

Candidates enroll in a course and study on demand. Instruction combines videos and written documents with downloadable calculation drills, detailed solutions, and interactive online exercises. The calculation workshop describes a progression from simpler exercises to more complex calculations.

A practical way to use this format is to:

• Study an explanation and identify the reasoning behind the method.
• Attempt the associated exercises before reviewing the solutions.
• Compare the calculation process, not just the final answer.
• Record recurring errors involving arithmetic, percentages, or magnitude.
• Revisit the method and apply it in a different business problem.

Treat this as a self-directed study routine. Reviewing a worked solution and receiving individualized feedback on a live interview are different activities; decide separately whether either kind of feedback is missing from the preparation plan.

Who May Find FastMath Useful?

FastMath’s emphasis on case calculations suggests several potential use cases, particularly where candidates understand the arithmetic concepts but want practice executing calculations with business-sized numbers.

• Candidates beginning case preparation who want a separate study block for numerical skills.
• Candidates whose calculations interrupt otherwise coherent case discussions and who want to isolate that weakness.
• Candidates refreshing arithmetic after relying heavily on calculators or spreadsheets.
• Self-directed learners who prefer working through explanations and exercises between mock interviews.

These are possible applications, not claims that every candidate needs additional math instruction. Someone already comfortable with case calculations can compare the syllabus with actual practice errors before allocating more time to quantitative drills.

How FastMath Can Fit Into Consulting Interview Preparation

One possible approach is to alternate focused numerical study with full case practice:

• Diagnose the difficulty. Separate arithmetic errors from problems with assumptions, equation setup, or interpretation.
• Select relevant material. Study the methods associated with recurring mistakes rather than repeatedly drilling calculations already handled comfortably.
• Apply the method in context. During a mock case, explain the calculation, work through it, check the result, and state its business significance.
• Reassess priorities. If numerical execution stops being the main limitation, redirect preparation toward other weaknesses.

This approach keeps calculation practice connected to the wider interview. Consulting case discussions also involve structuring problems, asking questions, analyzing information, and communicating reasoning—not simply producing numerical answers.

Reserve separate preparation time for personal experience and behavioral discussions. Official firm materials and sample cases can help establish the expected interview scope; McKinsey, for example, distinguishes its personal experience interview from its problem-solving interview.

What to Consider When Using FastMath

Review the particular course syllabus before selecting material. FastMath’s catalog includes both focused large-number calculation instruction and broader business-math courses, so the relevant scope depends on the course chosen.

• Match the resource to the difficulty. Ask whether the problem is arithmetic execution, selecting an equation, or understanding the business question.
• Plan active practice. Set aside time to attempt problems independently, rather than making lesson completion the sole objective.
• Identify the feedback needed. Decide whether checking solutions is sufficient or whether a practice partner should also assess the clarity of the explanation.
• Keep speed in perspective. Practice a pace that preserves clear reasoning. Case-interview guidance emphasizes communication and structured thinking and cautions against rushing responses.

A useful personal checkpoint is whether a method can be applied to an unfamiliar problem and explained clearly—not merely whether the lesson feels familiar.

Frequently Asked Questions About FastMath

Is FastMath a book or an online course?

The resource profiled here is an online course collection. Its delivery includes instructional videos, written materials, and calculation exercises rather than relying on a standalone textbook.

Does FastMath focus exclusively on consulting?

No. Consulting interview preparation is one application, but the curriculum also addresses numerical skills for other business interviews and workplace use.

What mathematical knowledge does FastMath assume?

The introductory calculation workshop lists single-digit multiplication, multiplication by ten, and an understanding of exponents as prerequisites. Candidates should check the requirements of their selected course.

Does FastMath cover market sizing?

Yes. The broader business-math curriculum includes market-sizing and estimation instruction, a framework, and worked examples.

Can FastMath replace fit or behavioral interview preparation?

It should be treated as numerical preparation, not a substitute for preparing personal examples. Behavioral and personal experience discussions address aspects of candidacy beyond calculation skills.

Can FastMath support consulting assessment preparation?

The provider describes its numerical material as relevant to tests with quantitative components. That does not establish that a course simulates a particular firm’s assessment. Confirm the exact assessment and its instructions before choosing test-specific preparation.