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# Brain teaser

Hi,

How to approach the measure of Eiffel tower weight?

Thank you!

Hi,

How to approach the measure of Eiffel tower weight?

Thank you!

(edited)

• Date ascending
• Date descending

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

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

(edited)

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

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

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:
• 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

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:
• 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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