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Mental Math

What is an easy way to calculate (1.04)^54?

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Top answer
Pedro
Coach
on Oct 12, 2021
Bain | EY-Parthenon | Roland Berger | Market Sizing | 30% discount 1st session

You need to know how to work with exponentials.

1^(a*b) = 1^a^b


1.04^54 = (1.04^9)^6 = ~1.4^6 = (~1.4^2)^3 = ~2^3 = 8

But… why do you ask? Howcome this is necessary in a case interview?

on Oct 13, 2021
It is a question from the case, Gravestone Inc.
Pedro
Coach
on Oct 13, 2021
Bain | EY-Parthenon | Roland Berger | Market Sizing | 30% discount 1st session
You are not expected to know how to do this type of mental calculation in an interview, so don't worry about it. You not expected to know financial heuristics.
Ian
Coach
on Oct 13, 2021
#1 BCG coach | MBB | Tier 2 | Digital, Tech, Platinion | 100% personal success rate (8/8) | 95% candidate success rate

Hi Cheryl,

Literally a waste of time to figure this out! This will not be in a case and this is definitely not what's expected in mental math! (Checkout the Preploung mental math exercises for a better idea…though even some of their advanced/hard ones are still too much!)

Anonymous A
on Oct 13, 2021
I disagree. They are likely testing if you know the rule of 72. At a 4% growth rate, an investment should double every 18 years. So over the span of 54 years, the investment should 8x (at a 4% growth rate).
Pedro
Coach
on Oct 13, 2021
Bain | EY-Parthenon | Roland Berger | Market Sizing | 30% discount 1st session
I disagree with you Anonymous A. You may see it in a casebook, but it would be complete absurd to ask this in a real consulting interview. Knowing math and arithmetics is a criteria to get into consulting. Knowing financial heuristics (e.g. the rule of 72) is not. May be a nice question for investment banking. Never for consulting.
Agrim
Coach
edited on Oct 22, 2021
BCG Dubai Project Leader | Elite Prep to dominate interviews | 10 years in Consulting + M&A | Free prep plan

Such specific questions are actually easier than they look - another method to solve this would be using the 72-rule

72 divided by % growth rate give you the time to double in years

Here, you are working with 1.04 which is nothing but 1 + 4%. So the question can be assumed as a 4% growth rate fund for 54 years

72 divided by 4% = 18 years

so in 54 years the money will double 3 times

After 18 years 1 will become 2 growing at 4%

After 36 years it will become 4

After 54 years it will become 8

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