Case Interview Math Practice: 30 Drills Under 60 Seconds (2026)

The 4 Core Math Skills

• ●Decomposition: Break the number into parts you already know.
• ●Rounding: 87 becomes 90. 415 becomes 400. State the round out loud.
• ●Benchmarks: Memorize cold: world population, India population, Indian GDP, typical margins per industry.
• ●Mental arithmetic: 3-digit times 3-digit without writing should complete in under 20 seconds.

Benchmarks to Memorize Before Any Case

• ●World population: 8.1 billion. US: 335M. India: 1.43B. China: 1.4B. EU: 450M.
• ●India GDP: $3.9T. US GDP: $28T. Global GDP: $110T.
• ●Typical margins: SaaS 75%, retail 30%, hardware 25%, banking NIM 3%, airline 5%.
• ●India urban/rural split: 35% urban, 65% rural.
• ●India smartphone penetration: ~70% of adults.

10 Market Sizing Drills

• ●1. Number of cars sold in India annually. (Target: ~4M)
• ●2. Revenue of Indian online grocery market. (Target: ~₹80K Cr)
• ●3. Number of Starbucks stores needed to saturate Bangalore. (Target: ~280)
• ●4. Annual UPI P2M transaction value. (Target: ~₹90 lakh Cr)
• ●5. Global Netflix subscription revenue. (Target: ~$34B)
• ●6. Number of software engineers in India. (Target: ~5M)
• ●7. Annual domestic flight passengers in India. (Target: ~170M)
• ●8. Annual coffee consumption in Mumbai in kg. (Target: ~4-5M kg)
• ●9. Revenue of Indian ride-sharing market. (Target: ~₹35K Cr)
• ●10. Number of EV two-wheelers in India. (Target: ~2.5M)

10 Profitability Drills

• ●11. Coffee shop with 80 daily customers at ₹180 ACV, 35% margin. Annual profit? (Target: ~₹18 lakh)
• ●12. SaaS at 5,000 customers, $100 ARPU/mo, 75% GM, $3M OpEx. Annual profit? (Target: ~$1.5M)
• ●13. Airline with 80% load factor, 180 seats, $200 fare, 5% margin. Profit per flight? (Target: ~$1,440)
• ●14. Hotel with 100 rooms, 65% occupancy, ₹5K ADR, 40% margin. Annual profit? (Target: ~₹4.7 Cr)
• ●15. Quick-commerce with 3,000 orders/day, ₹400 AOV, 15% contribution margin. Annual contribution? (Target: ~₹6.5 Cr)
• ●16. D2C skincare with ₹4 Cr revenue, 60% GM, 35% marketing, 15% ops. EBITDA? (Target: ~₹40 lakh)
• ●17. Payment gateway at 1B txns, ₹2 take per txn, ₹80 Cr opex. Profit? (Target: ~₹120 Cr)
• ●18. Food delivery platform at 50M orders, ₹50 take per order, 50% fulfillment cost. Contribution? (Target: ~₹1,250 Cr)
• ●19. Marketplace at ₹1,000 Cr GMV, 8% take rate, 55% contribution. Contribution profit? (Target: ~₹44 Cr)
• ●20. Fintech with 2M users, 30% paying, ₹500 ARPU/yr, 40% GM. Gross profit? (Target: ~₹12 Cr)

10 Growth and ROI Drills

• ●21. 100K MAU growing 8% monthly. MAU after 12 months? (Target: ~252K)
• ●22. $10M revenue growing 40% YoY. Year-3 revenue? (Target: ~$27.4M)
• ●23. Campaign with ₹50 lakh spend, 0.8% CTR on 50M impressions, 2% conversion, ₹1,500 AOV. Revenue? (Target: ~₹1.2 Cr)
• ●24. CAC $120, LTV $420, payback at 60% GM. Months to payback? (Target: ~10-11)
• ●25. Churn 2.5% monthly. Annual churn? (Target: ~26%)
• ●26. NRR: 100 starting ARR, 22 expansion, 7 churn, 4 contraction. NRR? (Target: 111%)
• ●27. Acquisition funnel: 100K visits, 4% signup, 30% activation, 12% paid conversion. Paid users? (Target: 144)
• ●28. Price increase 15% with 8% volume drop. Revenue change? (Target: +5.8%)
• ●29. A/B test at 18K vs 22K converters. Baseline 12% conversion. Lift? (Target: ~22%)
• ●30. Investment $500K, payback 24 months, discount 10%. NPV in year 3? (Approx, target: ~$180K)

How to Drill Daily

Set a timer for 60 seconds. Take one drill. State assumptions out loud. Narrate each step. Write only the intermediate numbers. Stop at the buzzer. Compare to target. If within 10%, you passed. If off more than 10%, redo slower tomorrow. 5 drills a day for 14 days and you will be at MBB speed.

Practice Case Math Live

ZeroPitch runs timed case math rounds with live narration scoring. See also McKinsey case examples and BCG case guide.