Re: Kiddie question


"Dean" <deanbrown3d@xxxxxxxxx> wrote in message
news:1172034504.398991.222160@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Imagine there are 1 billion couples, each on average having a 50%
chance of boys or girls.

Suppose after 10 years we wanted more girls than boys, for whatever
reason.

Each couple, for which their first kid is a girl, stops immediately.

If not a girl, they continue on until either they run out of time or
until they eventually fluctuate to girls > boys, stopping as soon as
girls > boys if it happens.

Do we end up with more girls this way?

Assume their is no biological effect other than 50% chance b/g each
time.

Can you be more specific?

What happens if there is a boy then a girl - do they stop?

And so on.

I did the same calculation with boys - see later.

If you stop when you have a boy - and have as many girls as you need until a
boy comes along then the average number of boys will be 1 and the average
number of girls will be 1.

I just used a spread***.

1 boy Prob .5
1 girl 1 boy Prob .25
2 girls 1 boy Prob 1/8
3 girls 1 boy Prob 1/16

Sum of probabilities=1

Average number of boys = 1 (every family has 1 boy)
Average number of girls = (1/4 +2/8 + 3/16 + 4/32 + ...)

I showed that the sum of the above series is 1 using Excel.

I am not clear what your simulation which took all night showed.

I did simulations in real time 30 years ago (eg a tennis game). I am not
clear why a simulation that you speak of would take all night these days.

Nick


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