OT BBC 'Maths' Quiz

Nice explanation, thanks
--
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Try thinking of it this way. You start with a solution space of four
possible answers {BB, BG, GB, GG}. Note that the *order* of the
letters is important and specifies the order in which the children are
observed.

By observing that the first child is a girl, the solution space
becomes reduced to {GB, GG}. That is, the probablity that the second
child observed is a girl is still 50%.

If instead of observing one of the children you had been told that at
least one of the two children is a girl then the solution space
reduces to {BG, GB, GG}. *Then* the probability that *both* children
are girls is 33%. Note also that the probability that the first child
is a girl is 66% as is the probability that the second child is a
girl.

If you *then* observe the first child and see it is a girl then the
solution space becomes {GB, GG} The knowledge that at least one of
the two children is a girl has become redundant as it adds no further
statistical information (a technical concept) to the knowledge that
the first obersevd child is a girl. We are then back at the first
case I described above.

The subtle difference is in making assertions about specific childen
or not.

I have the greatest respect for IS and his popular writings, so I
suspect there must have been a mistranslation of the question he
actually posed in said book. A link to the actual text would be
appreciated,

 

gomez wrote:

Thanks for that, it was simple enough to make things go *ding*.
Do you know of any stats books that keep things nice and simple, or
rather explain the complicated things in an easy to understand manner?

 

Re-reading the book, that is actually the situation that IS describes.

You're right - there was. My apologies to you and to those such as
Champ whom I've inadvertently attempted to mislead. I doubt it'll be
the last time.

<fx: profanities and chewing of knuckles>

 

Er ... I've found Ian Stewart is actually very readable - it's just my
memory of what he says is crap.

 

Afraid not. I forgot most of what I knew about statistics when I
leaft Uni in the 70's and found out there was more money in IT [1]
than in IT [2]. What I don't remember any more frightens me sometimes


[1] Information Technology.
[2] Information Theory (an esoteric branch of theoretical
statistics).

 

Never mind. Look on the bright side. Its a while since *I* have had
hold of the non-smelly end of the stick.

 

Statistics Crash Course by Murray R Spiegel is very good.
ISBN 0-07-052712-1

--
¤º°`°º¤ø,¸¸,ø¤º°`°º¤ø,¸¸,ø¤º°`°º¤ø,¸¸,ø¤º°`°º¤ø¤º°`°º¤ø,¸¸,ø¤º°`°º¤ø,

HAPPY CHRISTMAS !

ø,¸¸,ø¤º°`°º¤ø,¸¸,ø¤º°`°º¤ø,¸¸,ø¤º°`°º¤ø,¸¸,ø¤º°`°º¤ø¤º°`°º¤ø,¸¸,ø¤º°

 

It works if you tell someone "I have an X in my hand - what's the
probability of me having a second X" but not if you show them an X and
ask the probability of the other being an X.

I think.

 

Not quite

 

You have also removed BG leaving GG and GB so the answet is 1/2

 

What about false negatives?

 

That would be the 1% of the population that have it, but didn't get a +ve
result. 10%-9%

--
Catman MIB#14 SKoGA#6 TEAR#4 BOTAFOF#38 Apostle#21
Tyger, Tyger Burning Bright (Remove rust to reply)
Allfa 116 giulietta 3.0l (Really). Sprint 1.7
Triumph Speed Triple: Black with extra black bits
www.cuore-sportivo.co.uk

 

Dr Ivan D. Reid wrote

Oooh 'ark at 'er. Too good for the likes of us stuck at second level
calculus she is.

 

Right as you were then, it was 3 in the morning and I have only a hazy
memory of dribbling on the keyboard when I got in, that post was the result.
<checks sent boxthingy> yup that was it, I didn’t email my girlfriend
boss and tell him what I thought of him [1] I think that post was all I
managed before I collapsed.

[1] which given my state could have been anything from “I love you man”
to “You’re a prick”

--
Bob
Currently borrowing a black and red Yamaha XJ750 with fuel injection
Present: Honda XL125RF (FS)
Past: Honda CG125
bob at homeurl tomato dot co dot uk
remove the red fruit if you’d like to email me.

 

The sise of that Queen would make Portillo blush


--
Bob
Currently borrowing a black and red Yamaha XJ750 with fuel injection
Present: Honda XL125RF (FS)
Past: Honda CG125
bob at homeurl tomato dot co dot uk
remove the red fruit if you’d like to email me.

 

The size of that Queen would make Portillo blush


--
Bob
Currently borrowing a black and red Yamaha XJ750 with fuel injection
Present: Honda XL125RF (FS)
Past: Honda CG125
bob at homeurl tomato dot co dot uk
remove the red fruit if you’d like to email me.