[OK]

Privacy Policy  -  Terms & Conditions  -  See Details
We use cookies to personalise content and ads, to provide social media features and to analyse our traffic. We also share information about your use of our site with our social media, advertising and analytics partners who may combine it with other information you've provided to them or they've collected from your use of their services.

BB Logo
Spacer
Line
Line

Difficulty: EasyPuzzle Details

Suppose I flip two coins, without letting you see the outcome, and I tell you that at least one of the coins came up heads, what is the probability that the other coin is also heads?

Show Hint Show Answer Print Puzzle
[Ref: ZUYC]  

Answer: 1/3.

You might initially think that the answer is 1/2, however, it isn't.

Before I tell you anything, all you know is I've flipped two coins, and the possible outcomes are:

HH, HT, TH, TT

I now tell you that there was at least one head, which eliminates TT, leaving three possibilities. Of these three possibilities, only 1 allows the second head: HH. So the probability is 1/3. QED.


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 Escher type 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. We use cookies to personalise content and ads, to provide social media features and to analyse our traffic. We also share information about your use of our site with our social media, advertising and analytics partners who may combine it with other information you've provided to them or they've collected from your use of their services. For more information please view our privacy policy. By using the site you also agree to our terms and conditions.

Line
Line