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Mental Math - Exponent

Hi,

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

Thanks a lot!

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Top answer
Udayan
Coach
on Nov 23, 2020
Top rated Case & PEI coach/Multiple real offers/McKinsey EM in New York /12 years 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)

Allen
Coach
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?

Anonymous A
on Nov 23, 2020
Very helpful! It's good to know I don't need to focus on complex calculations
on Feb 02, 2024
How did you approximate that the initial value would be added again after 2 years?
Ian
Coach
on Nov 23, 2020
Top US BCG / MBB Coach - 5,000 sessions |Tech, Platinion, Big 4 | 9/9 personal interviews passed | 95% candidate success

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.

on Dec 30, 2020
McKinsey | NASA | top 10 FT MBA professor for consulting interviews | 6+ years of coaching

Hi, here you can find some good approaches to quickly crack it: https://www.preplounge.com/en/consulting-forum/estimate-compounding-4962

Best

Antonello

Gaurav
Coach
edited on Nov 28, 2020
#1 MBB Coach(Placed 750+ in MBBs & 1250+ in Tier2)| The Only 360° coach(Ex-McKinsey+Certified Coach+Active recruiter)

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

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