## 4 Engineering Students:

Four friends were brilliant engineering students. One day principal gave them a puzzle to solve. The four friends are lined up on some steps as shown below.
They are all facing in the same direction. A wall separates the fourth friend from the other three.

1. Friend 3 can see none of the others.
2. Friend 4 can see none of the others.
3. Friend 1 can see friend 2 and friend 3.
4. Friend 2 can see friend 3.
5. All are wearing hats.

They are told by the principal that two of them are wearing a white hat and two of them are wearing the black hat.
The friends initially don’t know what color hat they are wearing. They are told to shout out the color of the hat that they are wearing as soon as they know for certain what color it is.

## Rules:

1. They are not allowed to take their hats off.
2. They are not allowed to talk to each other.
3. They are not allowed to turn round or move.
Who is the first person to shout out and why?

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Friend 2 will shout first.
1. Friend 3 and Friend 4 will not be able to tell what color hats they are wearing since they cannot see the other men.
2. Friend 1 can see Friend 2 and Friend 3 but is not able to tell what color hat he is wearing as Friend 2 and Friend 3 are wearing different color hats. So Friend 1 will not shout out.
3. Then based on Friend 1’s silence, Friend 2 is able to interpret that he (Friend 2) and Friend 3 are wearing different color hats. Since Friend 3 is wearing a black color hat, so Friend 2 knows that he is wearing a white color hat.