Friday Puzzler -- two stickers

3/23/18, 2:47 PM #1

Alex Y
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Friday Puzzler -- two stickers

Alex Y

A logic professor created a test for her three top students. She showed them that she had eight stickers, 4 red and 4 blue. She then put two stickers on the forehead of each student and pocketed the remaining two. Each student could see the stickers on the other students' heads, but could not see their own (no reflective surfaces around!) or the two pocketed by the professor.

She asked them each in turn whether they know what color stickers are on their head. (They can hear each other's responses.)

A: "No."

B: "No."

C: "No."

A: "No."

B: "Yes."

What color stamps does B have?

Explain how you get to your answer

Re: Friday Puzzler -- two stickers

3/25/18, 5:29 PM #2

Larry Barrett
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Re: Friday Puzzler -- two stickers

Larry Barrett

B could have two stickers of the same color (RR or BB) or two different colors (RB). Even if B decided that he had two stickers of the same color, I don't think the question provides enough information for B to decide between RR or BB, so the answer must be that this is a trick question and B has RB.

Re: Friday Puzzler -- two stickers

3/26/18, 1:17 PM #3

Alex Y
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Correct :-)

Alex Y

I couldn't sucker you into doing it the hard way! Yes, this meta logic is the easiest way to solve this problem. In fact, it is possible to consider all the alternatives if person B had two of the same color. In each case, either someone could have made the determination earlier or person B would not have been able to make the determination when he did.

Friday Puzzler -- two stickers

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