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Mental Math - Exponent

Bain BCG Mck Quantitative skills
New answer on Dec 30, 2020
5 Answers
975 Views
Anonymous A asked on Nov 23, 2020

Hi,

How can I please calculate (1.25)^5 mentally?

Thanks a lot!

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Udayan
Expert
Content Creator
replied on Nov 23, 2020
Top rated Case & PEI coach/Multiple real offers/McKinsey EM in New York /6 years McKinsey recruiting experience

Not needed - if you ever see yourself with a problem like this either you have done something wrong or there is a simple way to do it (e.g., Rule of 72)

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Ian
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replied on Nov 23, 2020
#1 BCG coach | MBB | Tier 2 | Digital, Tech, Platinion | 100% personal success rate (8/8) | 95% candidate success rate

Allen has an excellent approach! The goal of math in casing is not to see if you can multiple super hard numbers together like an engineer. The goal is generally, can you figure out quick-and-dirty approaches to complicated situations, to get to the general answer that matters.

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Allen
Expert
replied on Nov 23, 2020
Ex-McK Experienced Hire and EM - I show you how to perform at your best

Don't worry about this! You will rarely have to do complex calculations in your head. Consultants don't need to do this.

Instead, what I'd focus on is that at a 25% growth rate, you'll double in approximately 3 years (due to rule of 72) and then add the same amount again in the next 2 years approximately (due compound growth). In summary, therefore, you can triple in 5 years, so the answer should be around 3. (In reality, when I calculate electronically, the answer is 3.05)

Does this help?

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Anonymous A on Nov 23, 2020

Very helpful! It's good to know I don't need to focus on complex calculations

Florian on Feb 02, 2024

How did you approximate that the initial value would be added again after 2 years?

Antonello
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replied on Dec 30, 2020
McKinsey | NASA | top 10 FT MBA professor for consulting interviews | 6+ years of coaching
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Gaurav
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updated an answer on Nov 28, 2020
Ex-Mckinsey|Certified Career Coach |Placed 500+ candidates at MBB & other consultancies

Hello! I agree that you do not need to make complex calculations in your head and that your approach to solve difficult problems is more important.
Hope it helps,
All the best
GB

(edited)

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