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Case interview prep in the age of AI

What eight employers, from Capital One to Grant Thornton, publish about the exhibits, numbers and written cases in their interviews, with five practice cases to work through.

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Start a practice case
North Quay Ferries · fictionalThe express charges £2 more a journey. Which service would you run?
One weekday of ferry operationsConventionalExpress
Forecast journeys400350
Journey capacity420360
Fare, GBP per journey57
Variable cost, GBP per journey23
Fixed cost, GBP per day9001050

Demand forecasts reflect each fare. Each fixed cost includes one vessel and crew.

Pick a service, then check it against the table.

Work it through in a practice interview

What statisticians and accountants say AI changes

The rules of the case

  • Grant Thornton
    • 22 minutes
    • Written report

    “You will have 22 minutes (not including any extra time that has been granted due to disability/additional needs) to review the case study information and write the report in the real assessment.”

  • Grant Thornton
    • AI tool built in
    • Up to 10 prompts

    “You'll review a set of business materials, write a recommendation and record two short videos. You'll have a built-in AI tool to help, with up to 10 prompts.”

  • KPMG
    • Calculator allowed
    • Strictly timed

    “You may use a calculator. The actual test is strictly timed. Try to complete each set of 4 questions within 3 minutes.”

  • PwC
    • No calculator
    • Mental math

    “Brush up on your mental math – no calculators allowed”

  • Capital One
    • Calculator when appropriate
    • Break-evens and algebra

    “There will be a quantitative element (e.g., break-even calculations, simple arithmetic, market sizing and algebra), but we allow calculators when appropriate.”

  • American Express
    • 2 minutes to structure
    • 1 minute to recommend

    “Save time for the analyses: don't take more than 2 minutes to structure your thoughts upfront and budget only 1 minute for reading out your recommendation; we care a lot more about the qualitative and quantitative analysis that takes place between these two steps”

  • EY-Parthenon
    • Ballpark estimates
    • Paper or whiteboard

    “You do not need to get a precise answer - use ballpark estimates as needed and work through the components of usage on a whiteboard or piece of paper.”

  • Deloitte
    • Spoken, written or both

    “In most cases, you will be asked to complete a case study based on a real or theoretical business scenario and resolve it verbally, in writing, or both.”

What employers say they’re looking for

01 Read the exhibit before you calculate

“Information can be presented in a range of ways, including text, tables, graphs, maps, and pictures. In this test, both qualitative and quantitative data is included.”

Grant Thornton UK, Early careers case study practice test · Grant Thornton, Undated

Find the rows that decide the question before you touch a calculator.

American Express’s practice case asks: “What insights can you derive from the charts above?” KPMG’s numerical test: “You will be presented with a series of tables and graphs, each followed by several questions. Your task is to choose the best answer to each question from the options given.”

  • American Express
  • KPMG
Case interview · Exhibit practiceWould a higher fare make the express ferry worth running?Example

02 Set up the math before you run it

“When working through a math problem, it’s helpful to first set up the problem and communicate your approach to your interviewer before proceeding with calculations.”

Capital One, Strategy Consulting candidate guidance · Capital One, Undated

Name the units first: an 800-job queue is not an 800-hour workload.

American Express: “Over-index on structure: whether it's writing algebraic formulas before executing math or bucketing qualitative insights into categories, structured thinking is critical for success” Capital One again: “There will be a quantitative element (e.g., break-even calculations, simple arithmetic, market sizing and algebra), but we allow calculators when appropriate.”

  • American Express
  • Capital One
Case interview · Exhibit practiceCan the team clear the winter repair backlog without overtime?Example

03 Estimate fast, with or without a calculator

“You do not need to get a precise answer - use ballpark estimates as needed and work through the components of usage on a whiteboard or piece of paper.”

EY-Parthenon Australia, Strategy graduate recruitment page · EY-Parthenon, Undated

Round to numbers you can carry in your head, then say how sensitive the answer is.

PwC: “During the interview, you may be asked to estimate figures or do quick calculations. Understanding and applying basic math, percentages and ratios can help you stay focused and confident throughout the conversation.” At Strategy& Middle East: “Brush up on your mental math – no calculators allowed” KPMG’s test allows one: “You may use a calculator. The actual test is strictly timed. Try to complete each set of 4 questions within 3 minutes.”

  • PwC US PwC
  • Strategy& Middle East (PwC) PwC
  • KPMG
Case interview · Exhibit practiceDoes the larger cold room produce the better result?Example

04 Write the recommendation, and question the AI’s draft

“Do you know when to rely on AI, when to question its output, and when your own thinking should take the lead?”

Grant Thornton UK, Early careers application process · Grant Thornton, Undated

Check what the draft left out before you accept its number.

Grant Thornton’s AI-enabled case: “You'll review a set of business materials, write a recommendation and record two short videos. You'll have a built-in AI tool to help, with up to 10 prompts.” Deloitte: “In most cases, you will be asked to complete a case study based on a real or theoretical business scenario and resolve it verbally, in writing, or both.”

  • Grant Thornton UK Grant Thornton
  • Deloitte Australia Deloitte
Case interview · Exhibit practiceDoes AI triage still save time after review?Example

05 Tie the numbers back to the decision

“Conceptual and numerical questions: identify the data needed, solve appropriate equations, and tie the data back to the problem.”

Capital One Canada, Strategy Analyst candidate guidance · Capital One, Undated

End with what the numbers mean for the choice in front of you.

Capital One: “Talk to them about your thinking, and be prepared to defend your answer with data.” American Express’s worked answer ends: “Takeaway: It would take longer than 3-years to break even on the investment” Deloitte: “Being able to show your work and explain your thought process during your interview can help set you apart”

  • Capital One
  • American Express
  • Keyana Dunn Deloitte Services LP
Case interview · Exhibit practiceIs the reachable market large enough to launch?Example

What the interviewer still wants to hear

Capital One: “proactively make grounded recommendations and rationalize your thinking.”

AI rules, by employer

  1. During the interview PwC: “The use of AI/GenAI during the assessment and interview process is not permitted.” Accenture lists as not permitted: “Using AI products during interviews to generate answers to questions for you.”
  2. Preparing Accenture: “Use AI to rehearse common questions”
  3. When the case includes AI Grant Thornton: “This assessment looks at how you read and interpret written content and data, and how you use AI to help you build and present a recommendation.” Strategy& Middle East: “Be ready to discuss how you use AI and digital tools effectively in your work or studies”

Policies as published; last checked Nov 11, 2026.

Sources

  1. Royal Statistical Society and Government Statistical Service, Joint roundtable report, The Future Statistician, at the time. Royal Statistical Society, “The Future Statistician: report of GSS and RSS joint roundtables”, Undated. Open the source. Checked against the published text.
  2. Donna Phillips, Chair, RSS AI Task Force, at the time. Royal Statistical Society, “AI is statistical. That matters.”, Undated. Open the source. Checked against the published text.
  3. Royal Statistical Society (AI Task Force), Policy paper, AI is Statistics, at the time. Royal Statistical Society, “AI is Statistics”, Mar 2, 2026. Open the source. Checked against the published text.
  4. American Statistical Association, Formal response to the US Department of Education, at the time. American Statistical Association, “ASA Response to Department of Education’s Proposed Priority”, Aug 20, 2025. Open the source. Checked against the published text.
  5. Paul Sweeting FIA C.Act, IFoA President, at the time. Institute and Faculty of Actuaries, “Financial services must confront ‘uncomfortable tensions’ in the Gen AI era”, May 28, 2026. Open the source. Checked against the published text.
  6. Helen Brand OBE, ACCA Chief Executive, at the time. ACCA, “AI driving increased use of real-time data by accountants enabling better business decisions, but integrity concerns widespread”, Undated. Open the source. Checked against the published text.
  7. Pete Brown, Global Workforce Leader, PwC, at the time. PwC, “AI reshapes global labour market into two distinct paths, rewarding human skills: PwC 2026 Global AI Jobs Barometer”, Jun 15, 2026. Open the source. Checked against the published text.
  8. Grant Thornton UK, Early careers case study practice test, at the time. Grant Thornton, “Early careers assessment guide (PDF)”, Undated. Open the source. Checked against the published text.
  9. American Express, Amex Strategy team practice case (US), at the time. American Express, “Strategy team practice case (PDF)”, Undated. Open the source. Checked against the published text.
  10. KPMG, Numerical analysis preparation guide, at the time. KPMG, “Numerical reasoning preparation guide (PDF)”, Undated. Open the source. Checked against the published text.
  11. Capital One, Strategy Consulting candidate guidance, at the time. Capital One, “Strategy | Interviewing”, Undated. Open the source. Checked against the published text.
  12. American Express, Amex Strategy team, at the time. American Express, “Strategy team practice case (PDF)”, Undated. Open the source. Checked against the published text.
  13. EY-Parthenon Australia, Strategy graduate recruitment page, at the time. EY-Parthenon, “Careers in EY-Parthenon Strategy, Transactions, Corporate Finance”, Undated. Open the source. Checked against the published text.
  14. PwC US, Advisory case interview candidate guidance, at the time. PwC, “PwC's student careers Website: Get Ready for Your PwC Case Interview”, Undated. Open the source. Checked against the published text.
  15. Strategy& Middle East (PwC), Business case prep page, at the time. PwC, “Ace your interview”, Undated. Open the source. Checked against the published text.
  16. Grant Thornton UK, Early careers application process, at the time. Grant Thornton, “Our application process”, Undated. Open the source. Checked against the published text.
  17. Deloitte Australia, Deloitte Life careers blog, at the time. Deloitte, “Preparing for a case study interview”, Undated. Open the source. Checked against the published text.
  18. Capital One Canada, Strategy Analyst candidate guidance, at the time. Capital One, “Interviewing for Strategy Analytics at Capital One Canada”, Undated. Open the source. Checked against the published text.
  19. Capital One, Careers blog, students and grads, at the time. Capital One, “4 tips to ace your Capital One case interview”, Undated. Open the source. Checked against the published text.
  20. American Express, Amex Strategy team practice case (UK edition), at the time. American Express, “Strategy team practice case (PDF)”, Undated. Open the source. Checked against the published text.
  21. Keyana Dunn, Senior experienced hire recruiting specialist, Deloitte Services LP, at the time. Deloitte US, “Preparing for the case and scenario interview”, Undated. Open the source. Checked against the published text.
  22. Capital One, Strategy Consulting candidate guidance, at the time. Capital One Careers, “Strategy | Interviewing”, Undated. Open the source. Checked against the published text.
  23. PwC, US Advisory case candidate guidance, at the time. PwC US Careers, “Get Ready for Your Advisory Case Interview”, Undated. Open the source. Checked against the published text.
  24. Accenture, Candidate AI-use guidance, US careers edition, at the time. Accenture US Careers, “Redefining hiring with the power of responsible AI”, Undated. Open the source. Checked against the published text.

Last reviewed Nov 11, 2026

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