Reply to: Google Interview Question - Probability

[RichardCranium]

Visualise the problem differently:

1. The first couple keep having babies until a boy is born.
2. Then the next couple start having babies until a boy is born to them.
3. Continue through the rest of the couples.

In this case, the couple gets replaced but the baby production just continues.

For each baby, the likelihood of it being boy/girl (50:50 or 52:48 or whatever) will not change.

So, the likelihood of boy / girl remains the same as it would if the couples continued having babies.

If all those couples' activities were then made concurrent, the ratio would still remain the same.


How's that for a solution & explanation?

[NotAllThere]

If you'd read just a little further, you'd find I'd said the same thing.

[Scary]

Only if I was an innumerate numpty.

I'd assume that the coin was double-headed, or some other trick. For a fair coin given a fair toss and discounting edge landings or other trickery of course you're right.

[NotAllThere]

You can get 4.5kg toblerone. Bet that would make anyone's eyes water.

[threaded]

I guess the answer isn't Toblerone - That would have to hurt!

But ribbed for pleasure.

[OwlHoot]

Ok mr Minestrone, Ms Ballbreaker from HR has a second question for you.

Ms BB - 'Mr Minestrone, if you were to have a chocolate bar shoved up your @ss, what type of chocolate bar would it be?'

I guess the answer isn't Toblerone - That would have to hurt!

[BrilloPad]

Ok mr Minestrone, Ms Ballbreaker from HR has a second question for you.

Ms BB - 'Mr Minestrone, if you were to have a chocolate bar shoved up your @ss, what type of chocolate bar would it be?'

I phone Marianne Faithful and she said a mars bar.

[NotAllThere]

I dont think that this is independent - Surely if a family has one girl then the probability of a boy next increases??

Similarly if I told you that I tossed 100 coins and each toss was fair and resulted in a tail would you not feel more bullish expecting a heads next??

Only if I was an innumerate numpty.

Nope - the outcomes are independent. What happens in one conception will have no effect on what happens in a subsequent conception...

True, but. Given that the chances of getting 100 heads is so low, if you were to get that, it's more likely that the coin isn't fair, or is being tossed in a way that changes the probabilities. Similarly, if someone has a run of daughters, then there is a possibility that they're producing more female sperm than male. Or that the male sperm are in some way defective. Or that the mother's "bits" are more hostile to male sperm etc. etc.

[bobhope]

It's all cobblers anyway, as there are about 106 boys born for every 100 girls and not 50/50.


So there.

[EternalOptimist]

Ok mr Minestrone, Ms Ballbreaker from HR has a second question for you.

Ms BB - 'Mr Minestrone, if you were to have a chocolate bar shoved up your @ss, what type of chocolate bar would it be?'

[NickFitz]

There is no answer, they want to see your thought process getting to an answer that cannot be found.

You are meant to be asking questions like "can you tell me what is the proportion of girls to boys born in this country?", "can you tell me what the proportion was before this rule is applied?" "How many families have reached the objective and how many have not?" "how many families are there?" instead of plugging in estimates to an equation like some of you have.

Myself, a degree trained engineer would grasp that but as most of you are not mathematically inclined then I see you are struggling with basic stats to answer a chaotic situation.

You have all failed.

You show promise, but some of your points are irrelevant, some betray an inability to understand obvious givens, and some are just stupid.

They're looking for "Smart and gets things done" - not "Smart and is totally up his own arse about it."

Try again in a couple of years when you've got some experience of solving problems rather than talking about them

[minestrone]

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?


Answers

There is no answer, they want to see your thought process getting to an answer that cannot be found.

You are meant to be asking questions like "can you tell me what is the proportion of girls to boys born in this country?", "can you tell me what the proportion was before this rule is applied?" "How many families have reached the objective and how many have not?" "how many families are there?" instead of plugging in estimates to an equation like some of you have.

Myself, a degree trained engineer would grasp that but as most of you are not mathematically inclined then I see you are struggling with basic stats to answer a chaotic situation.

You have all failed.

[Zippy]

Yeh, but it is not random but genetic on male side. In a population of 50 million say, what is to stop a woman having 96 billion girls before they get to a boy? Well, perhaps not 96 billion but one every 9 months from age 8 to age 70, that's 84 of em. Gawd, she'd have a fanny like the channel tunnel.

I think you'd have huge problems getting anywhere near the missus after child no 4
I believe sperm production in males is not entirely random (something I read, can't prove it) so the odds for a particular couple producing a male (or female) would not be 50/50

[EternalOptimist]

It has been shown that in an area with a female skew to the population the number of male births goes up, and vica versa.

They don't know the mechanism, just the statistics.

I just explained the mechanism, female on top equals more boys.

its a well known fact

[threaded]

It has been shown that in an area with a female skew to the population the number of male births goes up, and vica versa.

They don't know the mechanism, just the statistics.