classroom riddle

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As a test of intelligence, Puzzlefry academy sits two candidates in closed room.

The invigilator has three stickers, two white and one black.

Upon each of their foreheads he places a sticker at random, so that neither candidate can see their own sticker.

The candidate who identifies their own sticker first will be allowed entry into Puzzlefry academy.

After a few minutes, one of the candidates figured he had a white sticker. How?

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    Best answer

    Since there are TWO White stickers and only ONE Black sticker, there are only TWO possible ways to stick them on the two candidates: Either BOTH White OR ONE white and ONE black.

    If one of the candidates had a BLACK sticker on, the other candidate who can see the sticker can immediately deduce that (s)he has a WHITE sticker on (because there is only one black sticker which is already on the other candidate). But this did not happen, which means that both of them must be having a WHITE sticker.

    Viji_Pinarayi Expert Answered on 4th April 2018.
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