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Anonymous A
on Dec 30, 2019
Global
I want to receive updates regarding this question via email.

Brain teaser - babies born per year / month / day?

Hi All,

Could someone help me with this brain teaser:

"How many babies were born yesterday in the US?"

How would the answer change if the question would ask for the same value on a monthly or a yearly basis? 

Thanks a lot for your help!

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Top answer
Antonello
Coach
on Dec 30, 2019
McKinsey | NASA | top 10 FT MBA professor for consulting interviews | 6+ years of coaching

Hi,

  • US population: 320M
  • Life expectation: 80y
  • HP: Population equally spread for every age -> 0-1 years old: 320M/80 = 4M
  • Baby born in a day: 4M/365 = 11k

Best,
Antonello

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Luca
Coach
on Jan 02, 2020
BCG |NASA | SDA Bocconi & Cattolica partner | GMAT expert 780/800 score | 200+ students coached

I would follow the following process:

  • US population: 330M
  • US population "per year": 330M / 80 years = 4.1 M / year  Here you are making the hypothesis that the average life expectancy is 80 years
  • Babies born in a day: 4.1 M / 365 = 11 k 

Then you can state some aspects that cour estimation and add more complexity. For example:

  1. You could consider that natality is going down, adding a factor to decrease your number
  2. You can consider the natality distribution within a year: historically most of the brths are between July and September

Hope it helps,
Luca

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Theresa
on Apr 10, 2023
How can I consider the fact that the population is growing? Would that be correct if the population is growing 1% per year: #Population : life exp. + #Population x 0,01 ?
Deleted
Coach
on Dec 31, 2019
95% practise, 5% theory. We can make 2-3 real cases in a session or split the time 50:50 between case study and general background

Hi,

My logic would be as follows:

- There are about 300 mil. people living in the US

- Average family has 2 children (for simplicity) - in other words 1 child per person per life

- People live in average 70 years - lets asume, the amount of people in various age groups is equally split (i.e. same amount of people in age 1, same in age 31, same in 51 etc.)

==> 300 / 70 / 1 = 4 mil. children per year

==> 4 mil. / 365 = 11 tis. children per day

if you check it with the real statistics - its actually a very good yearly guess

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Sabina
on Oct 17, 2023

Hi all, 

I was wondering if I am applying to a consulting firm within the health care sector and they ask me "How many babies are born every year?", could I give the approach:

  • US population: 320M
  • Life expectation: 80y
  • Population equally spread for every age -> 0-1 years old: 320M/80 = 4M babies per year
     

Or is there another approach of how many babies are born in each hospital every year times the number of hospitals in the country?

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Clara
Coach
on Dec 30, 2019
McKinsey | Awarded professor at Master in Management @ IE | MBA at MIT |+180 students coached | Integrated FIT Guide aut

Hello!

I would go with: 

- Total population of the US: ~330 M people 

- Assume that people are equally distributed in the population pyramid from 0 to 90 years old. This makes 9 buckets of people (e.g., from 0 to 10, from 10 to 20, etc.) >> 330/9 = 36 M people in the 0-10 bucket. 

- Since natality is going down and you know the pyramid is not evenly distributed, you can go from those 36 M people from 0-10 to 30 M people. 

- Dividing 30 M people / 10 years, you obtain 3M people per year being born yearly in the last 10 years. 

- 3M people / 365 days you get approximately 8 K babies being born daily. 

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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