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The boy-girl puzzle
 

[Closed] The boy-girl puzzle

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im not being shouty and abusive??

So calling me a CRETIN and a PENARSE was a constructive argument was it?


 
Posted : 02/02/2009 4:47 pm
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I have 2 coins one in each hand one is a head what's in my left hand?

Good example.


 
Posted : 02/02/2009 4:49 pm
 Drac
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[i]Good example. [/i]

It's the simplest form to explain it but Bomberman's head must have exploded trying to prove 50/50.


 
Posted : 02/02/2009 4:50 pm
 Smee
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Drac - 50:50 chance its a head. 50:50 chance you have a head and a tail.

I was out playing in the snow.


 
Posted : 02/02/2009 4:52 pm
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Smee's back! We might get to 500 posts 🙂


 
Posted : 02/02/2009 4:53 pm
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drac its either a head or a tail


 
Posted : 02/02/2009 4:55 pm
 Drac
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[i]Drac - 50:50 chance its a head. 50:50 chance you have a head and a tail.[/i]

Read the question and you answer tell me what's wrong.


 
Posted : 02/02/2009 4:55 pm
 Drac
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[i]drac its either a head or a tail [/i]

Correct but please show the odds of what is likely.


 
Posted : 02/02/2009 4:56 pm
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head/head 50%
head/tail 50%


 
Posted : 02/02/2009 4:57 pm
 Drac
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[i]head/head 50%
head/tail 50%[/i]

How does that show what is in my left hand?


 
Posted : 02/02/2009 4:58 pm
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bomberman - you should probably read the other ten pages before you decide.


 
Posted : 02/02/2009 4:59 pm
 MTT
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Thankfully i don't post on here much these days and didn't get involved in this. Not read past the first page but here is my take;

BB - Disc
BG
GB
GG

So, 2/3 of mixed pair.

Ambiguity lies in the question and how you obtain the information about the child, if the mother is selected for her having a girl (ie. met mother and daughter) then the answer (by logic) is 1/2. But that doesn't apply here, because that wasn't the question.


 
Posted : 02/02/2009 5:00 pm
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you showed whats in your left hand - it was a head (LMAO!)


 
Posted : 02/02/2009 5:01 pm
 Smee
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Drac - it is a 50% chance that you will have a head in your left hand.

Following on from that there is a 50% chance that you will have a matching pair.


 
Posted : 02/02/2009 5:01 pm
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bomberman: Or tell me how YOU think the 100 families have after one child is born, and after two children.


 
Posted : 02/02/2009 5:01 pm
 Drac
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[i]you showed whats in your left hand - it was a head (LMAO!) [/i]

So you can't explain it then.


 
Posted : 02/02/2009 5:02 pm
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you showed whats in your left hand - it was a head (LMAO!)

No he didn't. He just said [i]one[/i] was a girl.


 
Posted : 02/02/2009 5:03 pm
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[b]MTT: [/b]Ambiguity lies in the question and how you obtain the information about the child, if the mother is selected for her having a girl (ie. met mother and daughter) then the answer (by logic) is 1/2. But that doesn't apply here, because that wasn't the question.

Correct MTT.


 
Posted : 02/02/2009 5:03 pm
 Drac
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[i]Drac - it is a 50% chance that you will have a head in your left hand.

Following on from that there is a 50% chance that you will have a matching pair. [/i]

No there's not all you know is there's one head, so it eliminates the T/T combination.

[strike]T/T[/strike]

H/H
T/H
H/T

Is the combinations you have left.


 
Posted : 02/02/2009 5:04 pm
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sorry my bad. it dosen't show what was in your left hand. is there a point to this? you'd better out it now before you forget.


 
Posted : 02/02/2009 5:06 pm
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you showed whats in your left hand - it was a head (LMAO!)

Drac's lack of punctuation is forgivable given that he is on nights, but it may be confusing you bomberman. He said [i]"I have 2 coins; one in each hand. One is a head. What's in my left hand?"[/i]

He didn't say which hand was holding the head.


 
Posted : 02/02/2009 5:06 pm
 Drac
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My lack of punctuation in confusing at the best of times.

[i]sorry my bad. it dosen't show what was in your left hand. is there a point to this? you'd better out it now before you forget. [/i]

Read what I put above and treat L/R how many time does head appear in L column?


 
Posted : 02/02/2009 5:10 pm
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it's the question.

So what are the odds that she has a girl and a boy?

in your eyes would the answer be different if the question said "so what are the odds that she has a boy and a girl?"


 
Posted : 02/02/2009 5:11 pm
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in your eyes would the answer be different if the question said "so what are the odds that she has a boy and a girl?"

Nope, the answer would be the same. 66%


 
Posted : 02/02/2009 5:13 pm
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In other words, contents of left hand is 50/50 for Head or Tail, Content of right hand is also 50/50 for Head or Tail

Possible combinations are:
[code]LEFT -- RIGHT
Head -- Head
Head -- Tail
Tail -- Head
Tail -- Tail[/code]

If you know he definitely has a Head in one of his hands then you can eliminate Tail -- Tail - leaving three possible combinations, two of which have Heads in his Left hand. 2 out of 3 = 66%

Nice example Drac.


 
Posted : 02/02/2009 5:16 pm
 Drac
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[i]Nice example Drac. [/i]

Thanks it makes it very simple though so some what kills the challenge.


 
Posted : 02/02/2009 5:17 pm
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[i]miketually - Member

Yes, but why would you ask her the original question?

So you can find out who the less intelligent people are.[/i]

What kind of smug coont makes a statement like that?


 
Posted : 02/02/2009 5:19 pm
 Drac
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[i]What kind of smug coont makes a statement like that? [/i]

A clever coont.


 
Posted : 02/02/2009 5:20 pm
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Drac, I think you've got a coin in your left hand.

BTW I queried the boy/girl girl/boy thing on page one, I understood the reason I was wrong before the end of the page.


 
Posted : 02/02/2009 5:22 pm
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girl/boy and boy/girl are the same, regardless of the 100 families theory. the fact that 100 families spawn 50% mixed, 25% bb and 25% gg has nothing to do with it. there are still 3 options to choose from and when you take them into the context of the question the other 99 families have absolutely nothing to do with it.

and by the way i just flipped a coin and it came out 70/30 in favour of tails, even though the odds were 50/50 so that puts your 100 families theory right out the window. when the question says it's a 50/50 chance it means biologically speaking.


 
Posted : 02/02/2009 5:26 pm
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yes but we're not talking about holding each child in a particular left or righ hand! you are adding a left/right variable that simply dosent exist in the original question! if you can't understand this then i guess i'm the more intelligent one!


 
Posted : 02/02/2009 5:29 pm
 Smee
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There is a 100% probability that a higher that average number of people involved in this thread have the memory of a gold fish and forget what they've just said.

Either that or there is one hell of an echo in here. 😀


 
Posted : 02/02/2009 5:29 pm
 Drac
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So not 2 coins then?


 
Posted : 02/02/2009 5:30 pm
 Drac
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[i]yes but we're not talking about holding each child in a particular left or righ hand! you are adding a left/right variable that simply dosent exist in the original question! if you can't understand this then i guess i'm the more intelligent one! [/i]

It does exist the combination is still there but some can't see that.

That and you were still convinced it was 50/50 for the coins.


 
Posted : 02/02/2009 5:32 pm
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read the question:

what are the odds that she has a girl and a boy?

not what are the chances that she has girl boy and not boy girl??


 
Posted : 02/02/2009 5:32 pm
 Drac
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[i]not what are the chances that she has girl boy and not boy girl?? [/i]

Or indeed "What are the chances she boy girl and not girl boy?"


 
Posted : 02/02/2009 5:33 pm
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It does exist the combination is still there but some can't see that.

i must be one of the blind ones then drac, or maybe you're looking for something that simply isnt there. if i had been so smug from the start of this thread i'd be looking for a way out of admitting i was in the wrong too.


 
Posted : 02/02/2009 5:34 pm
 Drac
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Thing was at the start you claimed it was 0.66 or 66%.


 
Posted : 02/02/2009 5:35 pm
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girl/boy and boy/girl are the same IN THE CONTEXT OF THIS QUESTION. the coins comparison does not work because it distinguishes between left and right which adds another variable. a variable which is not in any way aparrent in the OP.


 
Posted : 02/02/2009 5:37 pm
 Drac
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Sadly they're not the same combination but never mind.


 
Posted : 02/02/2009 5:37 pm
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girl/boy and boy/girl are the same, regardless of the 100 families theory. the fact that 100 families spawn 50% mixed, 25% bb and 25% gg has nothing to do with it. there are still 3 options to choose from and when you take them into the context of the question the other 99 families have absolutely nothing to do with it.

Yes they do - because you don't know which family you are dealing with and the distribution of those families mean that you are twice as likely to be dealing with a family that has mixed children

Just like in the 4999 girls/1 boy question - the other 4999 matter because they are what gives you the odds.

and by the way i just flipped a coin and it came out 70/30 in favour of tails, even though the odds were 50/50 so that puts your 100 families theory right out the window. when the question says it's a 50/50 chance it means biologically speaking.

F..k me. That's just not the way statistics works. It is 50/50 on every flip - that doesn't mean it will come out exactly 50/50 (otherwise every time you tossed a tail you'd know the next one would be a head).
70/30 is pretty normal variance for such a small sample size - flip it a million times and it will come out a bit closer to 50/50.

"Biologically speaking" the odds aren't actually 50/50 and many other factors effect the outcome.


 
Posted : 02/02/2009 5:39 pm
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Thing was at the start you claimed it was 0.66 or 66%.

yes because i was sure that the chances of it being a boy were higher as she had said she had a girl and i was thinking that that lowered the chances of it being a girl twice. I soon saw sense though

mixed
GG
BB (eliminated)

when you look at it like that it's really quite simple


 
Posted : 02/02/2009 5:40 pm
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It is 50/50 on every flip - that doesn't mean it will come out exactly 50/50

so why are you using the 100 families theory then?


 
Posted : 02/02/2009 5:42 pm
 Drac
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[i]when you look at it like that it's really quite simple [/i]

But wrong.


 
Posted : 02/02/2009 5:43 pm
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The PROBABILITY can be calculated exactly - even if small samples suggest it is something else.

If you throw a Head four times in a row, it doesn't change the probability - the next throw is still just as likely to come up heads or tails - anything else is the [url= http://en.wikipedia.org/wiki/Gambler%27s_fallacy ]Gambler's Fallacy[/url].

The 100 families example perfectly follows the exact probabilities because it makes it easier to calculate. I could have given you an example with 18.7 billion families where 9.238 billion have mixed, 4.616 billion have two boy s and so on, but I didn't think it would help. 🙂

Turn it into percentages from the start if you like: 100% of the families have no children. They spawn. Now 50% have a girl and 50% have a boy.
The ones with one girl spawn, (25% 2Girls, 25% Mixed) and the ones with one boy spawn (25% 2boys, 25% Mixed)

In total we now have:
25% of families have 2 Girls
25% of families have 2 Boys
50% of families have Mixed

Pick one random family and the likelihood of it having Mixed (50%) is twice that of it having 2 Girls (25%).


 
Posted : 02/02/2009 5:56 pm
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