Investment Banking Mental Math Practice Test

Banks screen candidates with two different mental math tests: standardized numerical reasoning platforms like SHL, Korn Ferry, or Kenexa in the early online-assessment stage, and unscripted, calculator-free mental math inside live technical interviews, where a wrong percentage or growth estimate can sink an otherwise strong answer. This page is the practice test. If you haven't built your core shortcuts yet, read mental math for finance interviews; here you'll drill ten fresh prompts plus three timed local reps.

TL;DR

• Numerical reasoning tests (SHL, Korn Ferry, Kenexa) run under strict time limits per question, usually under a minute each.
• The Round-and-Adjust Method rounds first, then corrects the estimate, instead of calculating exactly.
• A 5% growth rate compounded five times is close to 1.28x, not 1.25x; small compounding errors add up.
• Ten prompts below cover percentages, growth bridges, and multiple conversions.
• The local pack times three linked numerical reasoning categories back to back.

What is the Round-and-Adjust Method?

The Round-and-Adjust Method replaces exact multiplication with a rounded estimate, then a small correction, which is fast enough to survive a strict per-question time limit.

1. Round both numbers to the nearest clean figure (nearest 5, 10, or 0.5x).
2. Multiply the rounded figures for a fast first estimate.
3. Estimate the direction of the rounding error: did you round up or down on each number, and does that make your estimate too high or too low?
4. Adjust the estimate slightly in the opposite direction of your rounding bias.
5. State the estimate as a range if the prompt allows it, rather than a single falsely precise number.

Worked example: a percentage and growth bridge

Prompt: Revenue is 84 this year, growing at 12% a year. Estimate revenue two years from now, and state it as a percentage of a 100 target.

Round 84 to 85 and 12% to a clean multiplier of roughly 1.12 per year. Two years of compounding is close to 1.12 squared.

$$1.12^2 = 1.2544 \approx 1.25$$ $$85 \times 1.25 \approx 106$$

Since you rounded 84 up to 85, the estimate is slightly high; adjusting down gives roughly 105. As a percentage of the 100 target: 105 divided by 100 is 105%, meaning the estimate clears the target by about 5%. Stating "call it 105, so a little above target" is a faster and more useful answer than chasing a false-precision figure to the decimal.

Practice inside this guide

Numerical reasoning

Question 1 of 3

A target trades at $10.00. What offer price is a 20% premium?

Your answer

$/share

Check answer

The pack above times three linked categories, percentages, growth rates, and margins, back to back the way a numerical reasoning platform would. Time yourself against a clock, not just for correctness.

Ten more mental math prompts to practice

1. Estimate 17% of 240. Round 17% to 15% plus a bit: 15% of 240 is 36, and 2% more is about 4.8, so roughly 41.
2. A metric grows from 60 to 78. What's the percentage growth? 78 minus 60 is 18; 18 divided by 60 is 30%.
3. Compound 8% annual growth over three years. What's the rough multiplier? 1.08 cubed is close to 1.26, so about a 26% cumulative increase.
4. A company trades at 9.5x EBITDA of 42. What's the rough enterprise value? Round to 10x times 42, which is 420, then adjust down slightly for the 0.5x rounding, landing near 400.
5. Margin is 22% on revenue of 310. Estimate EBITDA. 20% of 310 is 62, and 2% more is about 6.2, so roughly 68.
6. A metric falls from 90 to 63. What's the percentage decline? 90 minus 63 is 27; 27 divided by 90 is 30%.
7. Estimate the square of 1.15, the kind of multiplier that shows up in two years of 15% growth. 1.15 squared is close to 1.32, so about a 32% two-year increase, slightly more than doubling 15%.
8. A deal is priced at 6.2x revenue of 55. What's the rough deal size? Round to 6x times 55, which is 330, then nudge up slightly for the 0.2x, landing near 340.
9. Estimate what percentage 34 is of 212. 34 over 212 is close to 34 over 210, or about 16%.
10. You're given a P/E of 14x and asked for the earnings yield. Earnings yield is the inverse of P/E: 1 divided by 14 is roughly 7.1%.
11. Estimate 23% of 340, rounding first. Round 23% to 25%: 25% of 340 is 85, then subtract roughly 2% of 340, about 6.8, for an estimate near 78.
12. A ratio moves from 1.8x to 2.3x over two years. What's the rough annualized growth rate? 2.3 divided by 1.8 is close to 1.28; the square root of 1.28 is roughly 1.13, so about 13% a year.

What to practice next

More timed reps across percentages, growth, margins, and multiples live in the drills library, filtered to markets and brainteasers. For the full shortcut library, see mental math for finance interviews. If your test is a data-table format, the numerical reasoning guide covers TRUE, FALSE and CANNOT SAY questions, and the brain teasers guide covers the estimation and logic prompts that sit next to the arithmetic.

Standardized test vs. interview mental math

Frequently Asked Questions

Which platforms do banks actually use for numerical reasoning tests?

SHL Numerical Reasoning, Korn Ferry Assessments, Cut-e (Aon) numerical scales, and Kenexa numerical reasoning are commonly cited platforms in the early online-assessment stage of banking recruiting.

Is a calculator allowed on these tests?

It depends on the specific assessment; some standardized numerical reasoning platforms allow an on-screen calculator, while live interview mental math almost never does. Follow the instructions you're given rather than assuming either way.

How precise does my mental math need to be in a live interview?

Close enough to be directionally correct and internally consistent. A stated, reasoned estimate ("roughly 105, so a bit above target") is usually more convincing than a suspiciously precise number you clearly didn't calculate live.

What's the fastest way to get faster at this?

Daily short reps on percentages, growth compounding, and multiple conversions, done under a visible timer, rather than occasional long study sessions. Speed comes from repetition of the same handful of shortcut patterns.

Do brainteasers test the same skill as numerical reasoning platforms?

Related but not identical. Brainteasers test composure and estimation logic under conversational pressure; standardized platforms test raw calculation speed and accuracy against a strict per-question clock.

What if I freeze on a mental math question in an interview?

Say your rounding approach out loud as you work through it. Interviewers are usually more interested in whether your process is sound than whether you land on the exact right number immediately.

How do I know if I'm fast enough?

There's no single published cutoff across banks, since standardized platforms and interviewer expectations vary. A reasonable internal target is answering each prompt in this test within 15 to 20 seconds while stating your rounding logic; if you're consistently slower, add a short daily set rather than one long weekly session.

Should I practice with a timer even for untimed study?

Yes. A visible timer, even a rough one, trains the habit of committing to an estimate instead of chasing exact precision, which is the actual skill both standardized tests and live interviews are checking.

Sources

• PrepLounge: online assessments in investment banking (checked September 2026).
• Wall St Math: mental math for investment banking (checked September 2026).
• Leland: a guide to mental math for your private equity interview (checked September 2026).