[rookie1ja]

Honestants and Swindlecants VIII. - Back to the Logic Problems
Thinking about the treasure, the gringo forgot what day it was, so he asked four aborigines and got these answers:
A: Yesterday was Wednesday.
B: Tomorrow will be Sunday.
C: Today is Friday.
D: The day before yesterday was Thursday.
Because everything you need to know is how many people lied, I will not tell. What day of the week was it?

Spoiler for Solution:

Honestants and Swindlecants VIII. - solution
The important thing was what we did not need to know. So if we knew how many people lied we would know the answer. And one more thing – B and D said the same.
If all of them lied, there would be 4 possible days to choose from (which one is not clear).
If only one of them spoke the truth, it could be A or C, so 2 possible days (not clear again).
If two of them were honest, it would have to be B and D saying that it was Saturday.
Neither 3 nor all 4 could have been honest because of an obvious conflict.
So it was Saturday.

[Anateresa]

It could also be the days they don't mention, like Monday, Tuesday, etc. Or not? Two people can be liars and give the same answer

[bama_moss]

Unfortunately the solution is based on the assumption that with the information given you can ALWAYS determine an EXACT answer. This is often left out on many of these logic puzzles.

Otherwise, Anateresa, you could be correct in concluding that it could be any day of the week. The description of this island should append the the following phrase:

After the inhabitants offer their answers you can always determine the exact truth.

[rofel_2612]

It is stated that in that place there are two kind of people:

Honestants.
-The one who said the truth.
Swindlecants.
-The one who tell lie.

In that case there are possible answer to this.
-Saturday.50%
-Thursday.25%
-Friday.25%

And the other days cannot be considered as an answer, because it will not meer the situation of having two kind of person. They all fall to the Swindlecants person.

[infomaniac.nick]

Quote

Honestants and Swindlecants VIII. - Back to the Logic Problems
Thinking about the treasure, the gringo forgot what day it was, so he asked four aborigines and got these answers:
A: Yesterday was Wednesday.
B: Tomorrow will be Sunday.
C: Today is Friday.
D: The day before yesterday was Thursday.
Because everything you need to know is how many people lied, I will not tell. What day of the week was it?

Because all you need to know is the number people which were lying, it stands to reason that the day with the unique number of people were lying is the correct answer

If the you were told that none of them were lying it could be Monday Tuesday Wednesday or Sunday.
Cannot be determined

If you were told that one of them were lying it could be Thursday or Friday.
Cannot be determined either.

Hence the only possible solution is Saturday
QED

[rijofl]

The solution given deals with Anaterasa's objection. If all of them lied it could be the days of the week not mentioned, and because it says there is a unique solution if you know how many liars there are, we know that none of the days not mentioned is correct because they don't provide a unique solution.

[Linzd21]

What if A, B, and D are liars and C is telling the truth. It is the only straight forward answer. Why does saturday have to be the day just because 2 people intimated that it was? If i were on and island and asked 4 people he same question survival and instinct and logic tell me to go with the guy that is not talking in circles to me. Honest people wouldn't do that. THE DAY IS FRIDAY

[eleftheria]

since the answer depends on the number of the liars we have 3 different situations:
(there cannot be no liars or only one liar because we would have no solution)
1)if 2 are liars then the correct answer is Saturday (because the other two have to be telling the truth)
2)if there are 3 liars then the correct answer is either Thursday or Friday depending on who says the truth
3)if all are liars then the day is Monday, Tuesday, Wednesday or Sunday

[PlayTheMindGame]

I really like these problems. XD
I worked it out and came up with Saturday, which I now see was correct. Yay!

[Steve Luke]

Linzd21, on Nov 15 2007, 11:31 AM, said:

What if A, B, and D are liars and C is telling the truth. It is the only straight forward answer. Why does saturday have to be the day just because 2 people intimated that it was? If i were on and island and asked 4 people he same question survival and instinct and logic tell me to go with the guy that is not talking in circles to me. Honest people wouldn't do that. THE DAY IS FRIDAY

This puzzle is real good. I got the right answer but for the wrong reason until I read some of the other posts.

The key is the problem states: "Because everything you need to know is how many people lied, I will not tell. What day of the week was it?"

If A B and D are liars then the number of liars (the only thing you need to know to get the right answer) is 3. But if we know there are three liars, there are two possible solutions. If A B and D are liars than the answer would be Friday. But B C and D could also be liars, making the answer Thursday. So there can't be 3 liars, or we would need more information to determine which 3 where the liars and the statement specifically says we only need the number of liars to get the correct answer.

So, given only the number of liars and the information in the problem the answer has to be Saturday, because it is the result of 2 people being liars producing a unique result, while all other counts for liars would produce non-unique answers.