Good morning guys; it is good to be back.
Pennsylvania is history and there is a while till May 6 in North Carolina
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What do we have here; a question Mark cannot answer? Oh boy, what a joy!
How about this; first label each person 0, 1, 2, ..., 6
Then label each color one through seven so that red is 1, orange is 2, yellow is 3...
When person zero looks at the other 6 people's hats he adds up their total and then guesses his hat so that the sum of all the numbers is zero in a mod-7 system.
Person 1 does the same thing but chooses his hat number so that the sum would be one in mod-7. This assures that there will be at least one person who guesses correctly because the sum of the colors must be 0-6 in mod-7.
So what I mean is:
As part of their strategy, the people agree to give each color a number, 0, 1, 2, 3, 4, 5 and 6. They also agree to work mod 7. They also agree to number themselves, in general order, from 0 to 6.
After the hats have been put on:
Let a_i be the color [number] of Person i's hat, (i from 0 to 6). Let S be the sum of all of their hats (S = sum of a_i from 0 to 6), modulo 7. Each person i assigns a value to s_i = the sum of all of the hats person i sees (mod 7)= sum of a_j for (j from 0 to 6 and j!=i) (mod 7) = S - a_i (mod 7).
Thus, a_i = S - s_i (mod 7). This is good, because each person knows the s_i that relates to him, and S is a constant. But, they don't know what the value of S is. But, they do know that S's value is only important modulo 7, and modulo 7 it can only have 7 values (0 .. 6). And, there are 7 people, each with a number i with the same range value as S. Thus, every person i guesses S is i, and guesses their hat color is a_i = S - s_i = i - s_i, the value of the last expression they can evaluate.
When guessing S is i, exactly one of the seven people will be right, and therefore exactly one will guess his hat color correctly, and they will win.
Ps; Thoh wrote, "
TTH, Tryst is Try"
Don't link me to that Australian joker!