[superprismatic]

Having given a shamefully incorrect knee-jerk answer to howardl1963's great little puzzle, "Guessing Coins", I would like to offer a

slight modification which, I think, points out the richness of this little gem. I hope howardl1963 doesn't mind that I have taken

his statement very nearly verbatim:

Bob offers Jim and Jack a gamble. Jim and Jack are allowed to discuss a strategy before hand, but won't be able to communicate in any way afterwards.

Jim and Jack will be put in separate rooms, with 1 fair coin each. Bob will go into one room, and ask Jim to flip his coin. He will then ask Jim to predict the result of the upcoming flip by Jack.

Bob will then go into Jack's room. He will ask Jack to flip his coin. He will then ask Jack to guess what Jim flipped. If BOTH of them guessed right, they each have to give Bob 10 dollars. If EITHER

of them are wrong, Bob will give them 1 dollar each. Should they accept the gamble?

[Guest]

This is a win win. All they have to do is - Jack says the opposite of what he flips and Jim says the same as what he flips. They will never be both right!

Here's how:

Four scenarios:

Jack-------Jim

1. Heads - Heads - Jack says Tails - Jack is wrong

2. Tails - tails - Jack says heads - Jack is wrong

3. Heads - Tails - Jim says tails - Jim is wrong

4. Tails - Heads - Jim says heads - Jim is wrong

I'd take this bet even if I had to bet my life on it (assuming I'm sure Jim doesn't wanna kill me :-))

Edited June 5, 2010 by HB921

[Glycereine]

This is a win win. All they have to do is - Jack says the opposite of what he flips and Jim says the same as what he flips. They will never be both right!

Here's how:

Four scenarios:

Jack-------Jim

1. Heads - Heads - Jack says Tails - Jack is wrong

2. Tails - tails - Jack says heads - Jack is wrong

3. Heads - Tails - Jim says tails - Jim is wrong

4. Tails - Heads - Jim says heads - Jim is wrong

I'd take this bet even if I had to bet my life on it (assuming I'm sure Jim doesn't wanna kill me :-))

by the time I typed mine it was posted

[Guest]

Very nice!

[Guest]

Nice thinking HB...

[Guest]

Thank you! My first reaction was No but then I gave it a thought and I was amused. Nice puzzle!

[Guest]

yes u r right bro........

Edited June 6, 2010 by onkar

[bonanova]

This is a variant of prisoners with hats where they are freed if one and only one guesses right.

It's a beautiful solution.