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In the advanced Nutripremium case:

Anonymous A asked on Sep 12, 2018

Assuming that a woman on average has 2 kids i.e. 18 months (1.5 years) in pregnancy. Assuming the average life span of a woman as 75 years. This gives me that on an average a woman will be pregant for 2% of those 75years.

How does that lead me to the conclusion that 2% of the women population will be pregnant at any given time.

Please suggest.

Thanks

(edited)

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Elias
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updated his answer on Sep 12, 2018
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Should be evident - maybe this will things clearer:

  1. imagine that all women were born on the same day and die on the same day.
  2. Now assume that a pregnancy will occur at a random point in their life (not between 20 and 40)
  3. Then at any given time, it can be expected that 2% of women are currently pregnant
  4. Now obviously not all women are born the same day - but obviously, pregnancies don't also occur at a random time in a woman's life. So the random time of birth "corrects" the non-random time of the pregnancy.

(As you should be able to guess by now, the 2% statement is only approximately true, as the age pyramid is not evenly distributed. But for case purposes it's close enough, I guess.)

(edited)

How does the correlation between 2% of time spent in pregnancy (18 months/75 yrs of avg life) and the population that will be pregnant work? How can one extrapolate the 2% avg time spent in pregnancy to 2% popn being pregnant. — Vikas on Sep 12, 2018 (edited)

Hi Vikas, to me it seems completely obvoius: if every woman during her life is pregnant for 2% of that lifetime, then at any given time 2% of the female population should be pregnant. I actually don't know how to put it in simpler terms. Maybe it'll help you to do the actual math (like with formulas)? — Elias on Sep 16, 2018 (edited)

Maybe try the same thing with school: Imagine a population of 750 people. The age distrbution is identical, so you have 10 people in very yearly cohort. Now assume that people spend 10 years in school, which is 10/75=13.33% of their lives. So there should be at any point in time 10 age cohorts of 10 people in school = 100 people. So 100 / 750 = 13.33%... Get it? — Elias on Sep 16, 2018

Obviously, this works for any size of population, if you assume that age distribution is spread equally among age cohorts. — Elias on Sep 16, 2018

i will try again. thank you for your time. i understand that it is a simple thing but i dont know what is that i have been missing that is reqrd to understand this. may be , i am finding it tough to correlate the time spent % to % of people. i appreciate yourhelp — Vikas on Sep 17, 2018 (edited)

Vlad replied on Sep 12, 2018
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Hi,

Here we also assume that all the population is spread equally among the age groups - it means that at any given moment we have the same amount of people of each age.

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Thank you. Agreed. But again it is the % of time spent on pregnancy i.e. 2%. But the solution says 2% of women population is pregnant at any point in time. How the avg time spent in pregnancy i.e. is 2% is extrapolated to 2% of population being pregnant. — Vikas on Sep 13, 2018 (edited)