Market-sizing & Guesstimate questions - Consulting Case Interview Prep


49 thoughts on “Market-sizing & Guesstimate questions – Consulting Case Interview Prep”

  • Although the structure of the problem is sound the solution is flawed. You are asked to find the number of people wearing red. If someone is wearing 1 piece of red or 5 pieces of red does not matter. It is still 1 person, so multiplying 2 pieces by 10% is completely wrong.

  • Gauri chaturvedi says:

    I had a question that what was the role of Monday in the problem which You did not consider in solving the problem.
    so the first thing that came to my mind was that Monday is a working day , and red is not the color that you generally wear at your workplace and the second thing was that shouldn't we divide it into males and females as it red is considered to be girl's color, and then further divide is working and non working population, Pleas do let me know if I am wrong with my approach.
    Thank you

  • Jesterday Jambi says:

    7:50 Apparently your own answer didn't ring any alarm bells in your brain lol, 12.2 million means more than half the people should wear red. Also your approach does not eliminate double counting. If someone wears two or more pieces of red clothing, you count them multiple times. The question doesn't ask how many pieces of clothing worn are red but how many people wear red.

  • dear Everyone,
    I know everyone is desperate to apply their calculations correctly, let me tell you this, YOUR RESULT, or IN FACT, THE CALCULATED ESTIMATED RESULT, DOESN'T REALLY MATTER TO THE INTERVIEWER. It's the approach. They aren't trying to judge what probability skills you can flaunt, they're there to judge what sort of approach you have applied. Please Calm down, and try not to focus on the end result!
    Thank you!

  • I was asked a ques in my Interview.
    How many footfalls you are expecting in a marathon organised in your city??
    Can you please suggest the solution for it

  • I think there's a mistake the author make.

    When you define "any piece is on a person is red is wearing red". Then, you don't times "# of pieces". Instead, you use 1-prob(not wearing red)^(total piece). Here's an example, your equation will be @home=5%* [1-(1-10%)^(2)]. The illogical part is the author counts 1 person wearing 10 red pieces as 10, which is equal to 10 people with each wearing 1 red piece.

  • McKinsey Vietnam has a low standard in their recruiting. Tip number 3: definitely could be more than 122mil if the chances of wearing red was higher since you have the multiple of clothing pieces lol…

  • How did you manage to come with the percentages like 10% wears Red & 5% sit at home, etc. That does not make any sense.

  • I am afraid I cannot follow your logic at all. For those who are going out twice, you are saying they have 10 pieces of clothing, with a 10% probability of each being red. Therefore you expect each person to have 1 piece of red clothing on them, which is absurd! You have managed to calculate the pieces of clothing that is red in NYC on a typical Monday (if that), not how many people will wear red.

  • Dear Kim, Thank you so much for these lovely videos. It has really helped me clear the prelim interview rounds with almost no other preparation other than your tutorials !Look forward to learning more from you! Regards.

  • What is a good source to think through different questions to get a flair of guessing and estimating within order?

  • Hi Kim, thanks for the video. small question- is it not required to state the rationale behind choosing the % of people ate home work etc ?

  • Utkarsh Raj Singh says:

    Hey Kim, I am trying to guess the market size for a fashion based social network in India. Where and how should I proceed for guesstimating the market size & opportunity ?

  • Your calculation about red is wrong. Other than that, great video. Third group should be named those who went out twice but did not wear red at the first time.

  • Alessandro Takeshi Morita Gagliardi says:

    Your math here is a bit flawed. If a person wears, say, 5 pieces of clothing, the chance that at least one of them will be red is 1-(0.9^5), i.e. one minus the chance none of their clothes is red, which is about 41%. Similarly, if they wear 10 pieces of clothing, their chance will be 1-(0.9^10) which is about 65%.

  • The answer is flawed. If people who are going out twice wear 12 pieces instead of 10, we will have the probability of wearing red equal to 120%, which does not make any sense. Actually, the answer shouldn't be using 10*10%; instead, it should be 1-0.9^10 = 0.65.

  • Thanks for taking out the time to make this video , but I am sorry to say that your calculations are completely wrong and this video needs to be taken down immediately , else you are going to misguide many people out here .I will just point out to one mistake and you can figure out the rest. for @home ppl you say they wear 2 pieces of dress and the chance of the colour is 10%. This means in order to calculate the total number of ppl possibly wearing red is 0.19*5 million. It is 0.19 because you need to calculate the probability of one of the suit pieces being red which has a 0.19 probability assuming only 10 colours are under use.

  • If chance is 10% and you got 2 pieces, it should be 1-(1-10%)^2 which is not so much different for 2 pieces, but if you got 10 pieces, then it's way different. If you have 12 pieces, then you are more than for sure wearing red?? No.

  • Parantap Singh says:

    Hey, nice video. I had a doubt. The question mentioned the number of people wearing red and not the number of red clothing articles that they are wearing. So, should we have multiplied the average number of clothes a person wears to get the final answer ?

  • Rodrigo Aoyagi says:

    Shouldn’t we consider the number of tourists visiting the NY Metropolitan area on a typical Monday in addition to the population?

  • Aditya Kondejkar says:

    1st of all video has cleared all my doubts
    having one problem
    I can't find link for e book of case studies .
    will you share it again?

  • New York City's population is 8.4m, NY State is about 20m. Just for your information…I like the way you do it tho. 🙂

  • Chirag Tibrewal says:

    There are sometimes supply side and demand side approaches being mentioned like McDonalds sale on a particular day can be calculated by the supply side or the demand side. Which one to follow when?

  • Sigbjörn Ekman says:

    NYC population is rather around 8.5 million while the state is about 20 million. Just for information. Doesn't affect the method you demonstrate 🙂

  • Do you have a resource or list of numbers we should memorize for estimation type questions (ie. population of the 5 largest countries in the world, population of NYC and LA, volume of a boeing 747, length/width/depth of a standard sedan, height of average skyscraper, etc.)?

  • I thought the interviewer said "do not count them twice", so that means in the scenario with people going out twice a day, and each time wearing 5 pieces of clothing, we should simply count it as 5 pieces of clothing and not 10 pieces right?

  • Let's say the chances of a piece being red is 20%, not 10%…
    Your answer would be 24.400 million people!
    How's that math ok?

    Even if the chances were 100%, your answer could not go over 20 million

  • Hooman Moayyed says:

    If I were the interviewer I would have failed you immediately for lacking a proper sanity check. According to your example, the chances of someone wearing red on a particular Monday would be 60%. Out of 10 colors and a 10% chance, The number should be no higher than 2 million.

  • Simone Buckinger says:

    Woah, this video is awful! Why does it get so many upvotes?!

    1) Completely wrong calculation!!! Chance of wearing red = 1 – chance of not wearing red = 1 – (9/10)^n pieces…
    2) No specific preference? Really? I don't think that i've got a single red pair of clothing… most socks are black, undies black or white or blue or green but not red, jacket not red etc…

    The whole calculation is retarded… With a simple "hm population is 20M and about every 5th guy/girl wears red so about 4M wear red" you'd be way closer. and about the clarification… what does it mean for a piece of clothing to be red? If I have a half red, half blue shirt is it red then?! Is my ketchup stain enough? Or does it mean completely red from A-Z?!

  • Smriti Mahendru says:

    Hi, In case I don't have any idea about my market size, what should be a approach ? For example you knew about 20 million population which is near true 23 million. For example if someone asks me "Estimate the quantity of wine consumed in Delhi in one year?, what will be an approach and answer ?

  • figures like NY population being 20mn are tricky….we need to know realistic assumptions here….any pointers? Why 20 mn?

  • Akash Deep Choudhury says:

    Correct me if I am wrong. I think there is a flaw in your answer. You multiplied %of people*no. of pieces*chances of being red to get the 'no. of people', which is incorrect. Think of it this way – Had there been a total population of 100 people wearing 3 pieces having 100% chances of wearing one piece being red, the answer will yield a total of 300 people wearing red which is greater than the total population! Correct approach should be %of people*chances. The number of pieces should be factored in while calculating the chance of wearing one red.

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  • Hi! In the last sector "going out twice" which constitutes 5 million people (or 25% of NY population), the number of people wearing red comes out to be 5 million. Doesn't it seem counter-intuitive? We took a group of 5 million people and our calculation shows that all of them are wearing red.

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