HTTPS

 If you experience any problems accessing the site using HTTP, you can try HTTPS by clicking the link on the left.

[OK]

Privacy Policy  -  Terms & Conditions  -  See Details
This website uses cookies. By using this website you are accepting the use of cookies.
For more information please view our privacy policy.

BB Logo
Spacer
Line
Line

Difficulty: MediumPuzzle Details

Puzzle IconI have two children. At least one of them is a boy.

What is the probability that both my children are boys?

My sister also has two children. The older child is a girl.

What is the probability that both her children are girls?

[Ref: ZFCA]

Show Hint Show Answer Print Puzzle
Direct Link: www.brainbashers.com?ZFCA

Answer:
If we list the possible combinations before we're told anything, and listing the eldest child first we have 4 possible outcomes:

Boy-Boy
Boy-Girl
Girl-Boy
Girl-Girl

Since I have two children, and we know that at least one is a boy, there are three equally probable cases: Boy-Boy, Boy-Girl or Girl-Boy. In only one case are both children boys, so the probability that both are boys is 1 in 3.

My sister's situation is different. Knowing that the older child is a girl, there are only two equally probable cases: Girl-Girl or Girl-Boy. Therefore the probability that both children are girls is 1 in 2.


Our Favourite Illusions

 Shadow Illusion
Are the squares A and B the same colour?

 Spinning Dancer
Which way is the dancer spinning?

 Impossible Waterfall?
Is the water flowing uphill in this impossible waterfall?

 The Butterfly
A colourful butterfly?

 Duck Or Rabbit?
Is this a duck or a rabbit?

 Hidden Faces
Can you find his three daughters as well?

 Blind Spot
An amazing demonstration of your blind spot.

 Impossible Prongs?
Impossible prongs?

 What Am I?
Can you tell what this is a picture of?

 Who Turned To?
Who is missing?

 Same Eyes?
Are her eyes the same colour?

 Parallel Cafe Wall Lines?
Are the horizontal lines parallel?

 



 

Line


BrainBashers™ is a trademark. This website uses cookies. By using this website you are accepting the use of cookies. For more information please view our privacy policy. By using this website you are also agreeing to our terms and conditions.

Line
Line