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## Math for fun and glory

### Course: Math for fun and glory>Unit 2

Lesson 1: Brain teasers

# Blue forehead room brain teaser

What happens when 100 perfect logicians have to figure out if they each have a blue forehead? Created by Sal Khan.

## Want to join the conversation?

• If I were there, I would simply just ask someone that I know if I am blue. The easiest way to solve it.
• All brain teasers are easy if you just ask for the correct answer, but then they wouldn't really be brain teaser.
• Sal mentions there are several applications for this type of problem can apply to. So what are they?
• Is logician really spelled that way?
• well, a logician is someone who uses logic, and when you type it in, it doesn't get highlighted red.
• ummmmm.........couldn't they just be able to scratch some of the paint off their own foreheads and see what color it is?
• it's a brain teaser you have to figure it out logically, and if you could scratch paint off your forehead and look at the color then Sal would have said so.
(1 vote)
• well if your forehead is blue and there is only 1 person with the blue forehead (its you) just look at everyone else's forehead so no one's head is gonna be blue so it has to be you.
(1 vote)
• True, but it probably won't be that easy; there will be more people with blue foreheads.
(1 vote)
• is the answer that they leave on the first black-out ?
(1 vote)
(1 vote)
• I thought that too and I was so excited 'cos I thought I'd figured it out but then I thought, "Isn't that a bit obvious and the solution is so complicated so I don't think that's it . . ."