IQ Test - here is another

[thunderlizard]

If 1 says nothing, 2 deduces 1 can see headphones of both colours. 2 sees 3 has red headphones, so concludes his is the opposite colour, and correctly shouts 'blue'.

how does 2 know there's somebody behind him?

[chef]

how much is the house worth they are sat in???

[realityhack]

I think you need to tell us more about what the four people know about the set-up. For instance that 2 out of 4 of them have red phones on and that two have blue? I know you have told us that, but I'm not clear how much of what you have told us has also been told to the 4 people.

they know eveything, except what colour they are wearing.
they can only see the dudes specified i.e. they cant turn their heads

this is a pure logic puzzle. One for Columbo

how does 2 know there's somebody behind him?

See above.

[thunderlizard]

oh right. Well done then Poirot!

[realityhack]

oh right. Well done then Poirot!

Merci, monsieur. Although I still don't know if that's the absolutely correct answer, it makes sense that way, to me.

[RichardCranium]

If 1 says nothing, 2 deduces 1 can see headphones of both colours. 2 sees 3 has red headphones, so concludes his is the opposite colour, and correctly shouts 'blue'.

Isn't that what I said, only longer?

[realityhack]

Isn't that what I said, only longer?

In essence, yes! I just put more words in there.