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Anonymous A
on Feb 17, 2021
Global
I want to receive updates regarding this question via email.

Brain teaser

Hi,

How to approach the measure of Eiffel tower weight?

Thank you!

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Top answer
Allen
Coach
edited on Feb 17, 2021
Ex-McK Experienced Hire and EM - I show you how to perform at your best

Remember, the key is to identify drivers, estimate the value, and use good judgement throughout.

Here's what I would do:  

Assume the majority of the weight will be the metal structure, not the stairs or the screws or the concrete base.  So we should focus on the weight on the metal.

Weight = density x volume for each "bar".  Density we would look up in real life, but for now we have to make some assumption. So now we have to estimate the volume of each bar and the number of each bar.

Volume is the interesting part.  Volume is area x height.  For Area, let's assume that all "bars" are 1 square foot, although for sure some are more and some are less.

So we still have to estimate the height of the bars.  How tall is the Eiffel tower?  Maybe 300 metres?  Maybe 1000 ft?  So we can calculate the volume of each bar.

Finally, the number of bars.  If I'm picturing it correctly in my head, we can say that the tower has 4 legs is made up of 4 vertical bars.  So total of 16 verticle bars, each 1000 cubic meters of volume.

There's probably also diagonal bars.  Maybe assume that for each vertical section of 4 bars there are 8 diagonal bars (making an 'X' shape up each side of each leg.  Assume they are like the hypotenuse of a right triangle so are approximately 1.4x as long as the height.  So it would be the equivalent of 8 x1.4 ~11 for every 4 bars.  So for the 16 vertical bars there will be 4 x 11 = 44 diagonal bars.  Therefore 16 + 44 = 60 bars of 1000 cubic feet.  There's probably also some horizontal bars, but let's assume these are thinner and negligable.

Now, I just multiplly it through:  60 x 1000 x Density.  Assume density of 250 kg per cubic foot.  Why 250?  I'm trying to picture a solid cubic foot of steel and how many people it would take to lift it.  If each person can lift 50kg, it would take 5 very strong people to lift, yeah that makes sense.  

Okay, so 60 x 1000 cubic feet x 250 kg per cubic foot.  So, multiply the last two terms first because it gives you a nice round number: 60 x 250,000 kg.  We know that 6 x 25 =150.  So 60 x 250,000 kg = 15,000,000 kg.

I'm trying to sanity check that, doesn't seem unreasonable.

Voila.  That was fun.  I have no idea if I'm right (or even in the ball park) but if I'm not, you can probably tell me which assumption(s) I made was incorrect, and fix it, which is exactly what is the point of a market sizing question.

Happy to help more, just message me!

Best,

Allen

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Ian
Coach
on Feb 17, 2021
Top US BCG / MBB Coach - 5,000 sessions |Tech, Platinion, Big 4 | 9/9 personal interviews passed | 95% candidate success

Hi there,

This isn't a brainteaser! This is a market sizing (though I know it doesn't sound like it)

General Tips for Market Sizing

  1. Just like in a case, make sure you understand the question - what are you really being asked to calculate
  2. Decide whether a top-down or bottom-up approach is best
  3. Figure out what you know you know, and what you know you don't know, but could estimate
    1. This helps you determine how to split out buckets
  4. Stay flexible - you can start with a "high-level" market sizing, but gauge your interviewers reaction....if it looks like they want you to do more...then go along level deeper in terms of your splits
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Clara
Coach
on Feb 18, 2021
McKinsey | Awarded professor at Master in Management @ IE | MBA at MIT |+180 students coached | Integrated FIT Guide aut

Hello!

This is a typical, not only with that building but, for instance, about the office you are in. 

There are a bunch: 

  • The easy ones: 
    • Google it
    • measure it in a picture where you have a referrence
  • The difficult ones 
    • Measuring the shade at some point of the day and figure out the height with trigonometry

Hope it helps!

Cheers, 

Clara

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Brainteaser
Brainteasers are a type of problem that focuses on a single issue rather than complex business cases. They require out-of-the-box thinking, logic or math skills and can take the form of riddles, word problems or visual puzzles. These tasks are designed to test your problem-solving skills, analytical thinking and ability to remain calm under pressure.Typical problems cover everyday life's topics and might even include unrealistic assumptions. All necessary information is usually included in the question so that further assumptions are not necessary. This article explains in more detail why brainteasers are useful in case interview preparation and how to solve them. Why Are Brainteasers Used in Case Interviews?First, in consulting case interviews, brainteasers are rarely used. Regular cases are considered more suitable as they allow the interviewer to better test key skills needed in a consultant (structured, analytical and conceptual thinking). However, brainteasers add significant value to the preparation process of several reasons:Enhancing Creative Thinking: Brainteasers demand unconventional solutions that go beyond the standard approaches used in typical business cases. This hones the ability to think outside the box and encourages flexibility in developing and applying different problem-solving frameworks.Building Stress Resilience and Speed: Brainteasers often place candidates under time pressure, mimicking the stressful situations commonly encountered in consulting. Regular practice with these challenges helps candidates remain calm and think clearly, even when the solution is not immediately apparent.Strengthening Mathematical and Logical Skills: Many brainteasers involve numbers or require logical deductions. Regular practice with these tasks improves the ability to quickly translate problems into mathematical or logical equations, a skill that is also valuable in complex business analyses.Avoiding Standard Solutions: By working on brainteasers, candidates reduce the risk of becoming too dependent on standard frameworks. This practice sharpens their ability to consider alternative solutions, which can be crucial in unpredictable business situations. How to Solve BrainteasersWhen approaching brainteasers, the method you use to tackle the problem is often more critical than arriving at the correct answer. Brainteasers test not only your creativity and logic but also your ability to structure your thoughts and communicate your reasoning clearly. By following a systematic approach, you can effectively break down complex puzzles and demonstrate your problem-solving skills: Structure Before Solution: The approach to solving a brainteaser is often more important than the final answer. Write down all the information provided, listen carefully, and make sure you haven’t missed or added anything. A structured approach demonstrates your ability to systematically analyze and tackle a problem.Brute Force: When a problem requires a specific number and the possible solutions are limited, a trial-and-error approach can be effective.Example: Replace 'x' with the digits 1, 2, 3, 4, 5, and 6 to make the equation xx * x = xxx true. Solution: 54 * 3 = 162.Logic: Many brainteasers can be solved by logically interpreting the information given and drawing the correct conclusions.Example: Five friends have 10 cookies. They vote on how to split them in alphabetical order. Anyone who doesn’t get at least 50% of the votes is out. Anton votes first. The maximum number of cookies he can demand is 8. Key Takeaways - What Brainteasers Are Useful ForBrainteasers are not common in case interviews but are highly useful for preparing for unconventional problem-solving situations.They enhance creative and structured thinking, build stress resilience, and improve mathematical and logical skills. Brush up on your mental math skills. Being quick and accurate with numbers is crucial!Focus on the problem-solving process and structure rather than just finding the correct answer. 
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