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Choose random between two option.

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Giselle
Giselle 2017-3-23
评论： Valerie Reinisch 2020-12-22

Hi, i want to choose randomly between the "boy" or "girl", how can i do that? Each has the same probability of 50%.

i want to calculate this question:

In a country in which people only want boys … … every family continues to have children until they have a boy. If they have a girl, they have another child. If they have a boy, they stop. What is the proportion of boys to girls in the country? Tnx

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回答（2 个）

Image Analyst
Image Analyst 2017-3-23
Hint:
sexes = {'Boy', 'Girl'};
r = randi([1, 2], 1) % Get a 1 or 2 randomly.
thisSex = sexes(r) % Extract the sex for this random number.
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Walter Roberson
Walter Roberson 2020-12-22
编辑：Walter Roberson 2020-12-22
r = rand() > 0.60
thisSex = sexes{r+1}
By the way: my modeling says 2/3 girls on average.
Valerie Reinisch
Valerie Reinisch 2020-12-22
Tried it in the meanwhile with this:
r = binornd(1,0.6)
But thanks a lot for this quick answer! (:

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Roger Stafford
Roger Stafford 2017-3-23
编辑：Roger Stafford 2017-3-23
There should be no need to go through such a simulation. For each birth the probability that a boy is born is one-half regardless of all the tricks the family may play.
However if you are addicted to more complicated computations, the average number of boys per family is:
1/2*1 + 1/4*1 + 1/8*1 + ... = 1
and the average number of girls per family is:
1/2*0 + 1/4*1 + 1/8*2 + 1/16*3 + 1/32*4 + ... = 1
You can use symsum to verify these.
  1 个评论
Walter Roberson
Walter Roberson 2020-12-22
Ran in:
trials = 1E6;
isboy = rand(trials,53) <= 0.5;
child_number_for_boy = sum(cumprod(~isboy,2),2) + 1;
avg_number_of_girls = mean(child_number_for_boy - 1)
avg_number_of_girls = 0.9988
max_number_of_girls = max(child_number_for_boy) - 1
max_number_of_girls = 20

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