The Question is Describe the strategy. Red/Black Forehead Dots: A group of 20 pe

Question

The Question is Describe the strategy.

Red/Black Forehead Dots:

A group of 20 people got kidnapped and are held in a cell. The kidnapper tells them that each of them will be given sleeping pills and at night each will marked on their forehead with a red or black ink dot. Tomorrow, after waking up each one will be able to see all foreheads
except one's own but no talking or signalling will be allowed. Then kidnapper will choose the first victim to guess the color of dot. The first victim will say "red"or "black" and will be spared or executed depending on his correct or wrong guess. Then the next victim will be chosen by kidnapper and so on.

The problem is that in the remaining evening time before sleeping to come up with a strategy that will guarantee that all will be spared but one who may be spared or may be executed.

The Question is Describe the strategy.

Explanation / Answer

The stratergy is simple.

They will fix one color for "even" and other for "odd".for example blue for "even no of blues" and red for "odd no of blues"

so if the first person says"blue".he is aknowledging others that he is seeing even no of blue dots or he shouts red if he sees odd no of blue dots. so that the every person can caluclate their color.

For example if the first person shouts blue that means he is able to see even no of blue dots.and every other person can see all other foreheads so they can see no of blues on others foreheads .if the no of blue dots on other foreheads is even that means his color is red else his color is blue

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