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### Topic: Faites vos jeux messieurs, dames (Read 5786 times)previous topic - next topic

#15
##### Aug 24, 2013, 06:12 pm
PART 1 - I have two children. One of them is a boy. What are the odds that the other is also a boy?
@robtillaart correctly answered 1:3 or 33% (he also jumped the gun a bit on the next part)

So now onto the interesting bit;
PART 2 - I have two children. One of them, the thinnest, is a boy. What are the odds that the other is also a boy?

Cards on the table folks.

#### mmcp42

#16
##### Aug 24, 2013, 06:17 pm
You probably want to say same as case 1
there are only 10 types of people
them that understands binary
and them that doesn't

#17
##### Aug 24, 2013, 06:54 pm
Quote
You probably want to say same as case 1

No I want you to tell me if the fact that this time the boy is thin changes the odds or not.

#### mmcp42

#18
##### Aug 24, 2013, 07:23 pm
Odds unchanged
there are only 10 types of people
them that understands binary
and them that doesn't

#19
##### Aug 24, 2013, 07:58 pm
Messieurs, dames - the first bet has been placed that skinny children don't change the odds.
Get your money on the table.

#### Nick Gammon

#20
##### Aug 24, 2013, 11:33 pm
Are we talking probability here or DNA? You mentioned DNA in the first post.
Please post technical questions on the forum, not by personal message. Thanks!

http://www.gammon.com.au/electronics

#### Nick Gammon

#21
##### Aug 25, 2013, 03:19 am

So now onto the interesting bit;
PART 2 - I have two children. One of them, the thinnest, is a boy. What are the odds that the other is also a boy?

I would say 1:2 chance.
Please post technical questions on the forum, not by personal message. Thanks!

http://www.gammon.com.au/electronics

#### Nick Gammon

#22
##### Aug 25, 2013, 04:42 am
My justification is along the lines of reply #10.

Assume we have four possibilities:

Code: [Select]
`TB GTG BTB BTG G`

Where T stands for thinnest.

Given that we know that we have TB (thinnest/boy) then we are left with:

Code: [Select]
`TB GTB B`

Only two left, so there is a 50% possibility of a girl.
Please post technical questions on the forum, not by personal message. Thanks!

http://www.gammon.com.au/electronics

#23
##### Aug 25, 2013, 10:13 am
Quote
Are we talking probability here or DNA? You mentioned DNA in the first post.

Nothing to do with DNA just probability.

This truth table is incorrect for several reasons by the way
Code: [Select]
`TB GTG BTB BTG G`

#### Nick Gammon

#24
##### Aug 25, 2013, 10:23 am
Your claim is incorrect however the proof is too large to fit in the margin.
Please post technical questions on the forum, not by personal message. Thanks!

http://www.gammon.com.au/electronics

#### robtillaart

#25
##### Aug 25, 2013, 12:01 pm
Quote
Nothing to do with DNA just probability.

Always understood that the way DNA combines (to create a new creature great or small) has a lot to do with probability.
I recall studying Mendel's probability law's with drosophila melanogaster (fruit fly) during biology.
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

#26
##### Aug 25, 2013, 01:40 pm
We have two bidders one that the skinny boy does not change the odds at 1:3 or 33% and the other that the boy being skinny does change the odds to 1:2 or 50%.

Any one else going to take a side?

#### robtillaart

#27
##### Aug 25, 2013, 02:04 pmLast Edit: Aug 25, 2013, 02:07 pm by robtillaart Reason: 1
I'm with Nick (#22) => 50%
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

#28
##### Aug 25, 2013, 08:09 pm
Nick and Rob have the right answer 1:2 50% though Nick's reasoning was not quite correct - will post post full answer later.

Is it not bizarre though;
If I tell you I have two children one of whom is a boy the odds of me having two boys is 1:3 33%, yet if I tell you I have two children one of whom is a boy who happens to also be my thinnest child the odds of me having two boys is 1:2 or 50%.

No tricks, no genetics, just maths!

#### robtillaart

#29
##### Aug 25, 2013, 09:28 pm
Another riddle: (this one took me some time)

A man has three children.
The product of their ages is 36.
The sum of their ages is the number of cars in my street.
And to determine their ages you must know that the youngest was ill recently.
How old are the kids?

(yes you need al the information)

Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

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