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

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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!

5 Answers

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Top answer

Antonello

on Dec 30, 2019
Coach

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

0 comments

Luca

on Jan 02, 2020
Coach

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:

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

Hope it helps,

Luca

Anonymous

on Dec 31, 2019
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

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?

Clara

on Dec 30, 2019
Coach

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 yearl**y 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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Top Answer by

Antonello

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McKinsey | NASA | top 10 FT MBA professor for consulting interviews | 6+ years of coaching

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