Is a married person looking at an unmarried person?

Question

I remember answering this one incorrectly and when the answer was explained to me I was annoyed with myself. Here is your chance, with the original word phrasing:

Jack is looking at Anne, but Anne is looking at George. Jack is married, but George is not. Is a married person looking at an unmarried person?

A) Yes
B) No
C) Cannot be determined

The first with the correct alternative with the correct logical explanation ... (you know the drill).

So, out of curiosity, how did you answer it, and what was your reasoning? — Dan Henderson, Aug 19 '16 at 15:05
@DanHenderson I answered that it could not be determined just because we do not know if Anne is married or not. According to http://magazine.utoronto.ca/feature/why-people-are-irrational-kurt-kleiner/ this is the same as the majority answer. — Halvard, Aug 19 '16 at 16:40
Wait, this question wasn't asked before on this site?? It's a famous puzzle... — Sid, Aug 19 '16 at 16:43
I know this puzzle from here: https://www.youtube.com/watch?v=tO8d60nM5k4 — manshu, Aug 20 '16 at 18:44
It's worth noting that this puzzle assumes that a person can only be married or unmarried - that is, that they're complementary states. For instance, if one admits "divorced" as a separate category, then the answer is "C", as Anne may be divorced. — Glen O, Aug 21 '16 at 05:25
@GlenO All divorced people are still either "married" or "unmarried", it just depends on whether or not they remarried since the divorced. If Anne is divorced the answer is still "A". She is either divorced and unmarried or divorced and married, but no matter what a married person is looking at an unmarried person. — Paul, Aug 21 '16 at 18:20
This is getting silly. Stop tryinng to find loopholes. "What if Anne is neither married nor not married?". I say what if Anne is a bird and the concept of married does not apply? What if Jack is jack daniels, Anne is Queen Anne and George is George T. Stagg and the OP just drank all of them and is drunk when writing this question? Everyone understood the idea in this question. No need to try and dissect it. Just enjoy it and move on. Or simply move on. — Marius, Aug 21 '16 at 18:28
@MyStream: The question is not whether Anne is married, but whether there is someone who is married, who is looking at another person who is unmarried. If there is definitely such person, the answer should be "Yes". If there is definitely no such person, the answer should be "No". Otherwise, the answer should be "Cannot be determined". — justhalf, Aug 22 '16 at 03:56
@Paulpro - it depends on the language being used. Oftentimes, in legal documents, "divorced" is a separate category. Note that I'm not asserting that the correct answer is "C" - just that there's an assumption being made that isn't explicitly stated. — Glen O, Aug 22 '16 at 10:15
@MyStream we know the status of both Jack and George by the statement. Then, we do not need to know Anne's to answer, since no matter what it is the answer is the same (yet for different reasons). — Clement C., Aug 22 '16 at 13:08
@MyStream. You sound like a Trump speech. "Who says where are we allowed to look or not? We should make Puzzling SE great again and everybody should be able to look at everybody without being asked of their marital status". Dude...it states clearly in the question. Jack looks at Anne, Anne looks at George. It's NOT about who's allowed to do so or not. It's a fact not a question. The question is, among these 2 looks, is there one where the person that does the looking is married and the person that is seen is not married? Simple as that. — Marius, Aug 22 '16 at 13:18
If you want a loophole it's easy: nowhere does the question state that any of Jack, Anne or George is "a person", but the question is about "a person" looking at someone. If you genuinely don't understand the question, that's fine, but there's two possible solutions: tighten the language of the question, or improve your own reading comprehension :-) The conclusion is that any question that doesn't precisely define all terms used is unanswerable. Given how the English language works, this conclusion unfortunately is boring. — Steve Jessop, Aug 23 '16 at 09:51
@MyStream. First of all I am sorry if my comment looks acid. I read it again and you are right. It can be interpreted as that. It was not my intent. I was trying to have some fun. If you would have seen my face when I wrote it you would understand. Also, I accumulated some frustration seing a lot of dissected questions in here and slightly snarky comments are a way of blowing a bit of steam. I mean no disrespect to anyone. And just for the record...I don't have any political views. — Marius, Aug 23 '16 at 16:34

Smart · Accepted Answer · 2016-08-19T13:30:42.187

93

Answer is

YES.

because,

If Anne is married, she’s looking at George, who is unmarried. If Anne is unmarried, Jack is looking at her.

edited Aug 19 '16 at 13:30

answered Aug 19 '16 at 13:29

Smart

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It also works for arbitrarily long chains of people, as long as the first is married and the last is not. For any binary string starting with 1 and ending in 0, there must be at least one 10 somewhere. – Clement C. Aug 19 '16 at 15:47
@ClementC. Of course, this is only definable at such (the fact that you can pick a place to start which is 1) as this system is a cycle. – Weckar E. Aug 22 '16 at 12:10
As a red-herring, but to create a full cycle: you could also have the last person looking at the first. – Paul Evans Sep 11 '19 at 16:42

Marius · Answer 2 · 2016-08-19T13:51:18.210

26

Answer:

A) Yes.

Reasoning:

Case 1. Anne is married. Then Anne (married) is looking at George (not married).
Case 2. Anne is not married. Then Jack (married) is looking at Anne (not married).

edited Aug 19 '16 at 13:51

answered Aug 19 '16 at 13:29

Marius

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In scenario 2 I think you mean anne is unmarried – Beastly Gerbil Aug 19 '16 at 13:49

score 19 · Answer 3 · answered Aug 19 '16 at 15:50

19

Answer:

Cannot be determined

Because:

There may be two Anne's, the first may be married and the second not.

answered Aug 19 '16 at 15:50

Joe

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Good point haha :) – Kevin Aug 19 '16 at 17:07
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@Kevin Good if the question were tagged lateral thinking, not so much for logical deduction. – Mike Kellogg Aug 19 '16 at 21:21
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Seems like it ought to be specified that there are only 3 people, no? – Joe Aug 19 '16 at 21:38
Nice one, although this only works if the two Anne's were not connected in a line of "looking at's" (Jack->Anne1->Anne2->George), otherwise you would get a "yes" where Anne1 looks at Anne2. If we don't know if Anne1 may or may not be looking at someone, the "can't be determined" holds. – Megha Aug 21 '16 at 01:04
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the language strongly suggest that it's the same Anne so you can't assume there are 2. – adhg Aug 21 '16 at 18:36
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The term unmarried does not mean not married, there could be an ambiguous state in between with the right context. Jack may not be a person, but rather a robot. This question may be written in another language where words mean something completely different. Logic itself lies on unproven axioms, and without a proof of those axioms we cannot know it is consistent, and in an inconsistent system any statement is true. The world has billions of people, and certainly somewhere an unmarried person is looking at a married person. -1, you could do better. – Yakk Aug 22 '16 at 13:36

score 14 · Answer 4 · answered Aug 19 '16 at 17:06

Answer:

A) Yes

Because:

Say the symbol -> stands for 'is looking at'. So Jack -> Anne -> George. If we replace the names of Jack and George with either married of not married, we get married -> Anne -> not married. Since Anne can be married or not married, the possible cases are married -> married -> not married and married -> not married -> not married. In both possible cases a married person is looking at an unmarried person. So the right answer is A.

Michael Mrozek · Answer 5 · 2016-08-22T08:14:03.160

8

Proved the answer in coq:

Inductive person : Type :=
  | jack : person
  | anne : person
  | george : person.
Parameter married : person -> bool.
Parameter looking_at : person -> person -> bool.
Goal
  looking_at jack anne = true ->
  looking_at anne george = true ->
  married jack = true ->
  married george = false ->
  exists p q, married p = true /\ married q = false /\ looking_at p q = true.
Proof with auto.
  intros.
  destruct (married anne) eqn:H3.
    (* Anne is married )
    exists anne, george...
    ( Anne is unmarried *)
    exists jack, anne...
Qed.

edited Aug 22 '16 at 08:14

answered Aug 21 '16 at 02:08

Michael Mrozek

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Please check it's all still aligned as you expect. – Jonathan Allan Aug 22 '16 at 03:53
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@JonathanAllan Ah, nice. Had to escape some *s, but otherwise good. Thanks – Michael Mrozek Aug 22 '16 at 08:14

score 7 · Answer 6 · edited Aug 22 '16 at 03:51

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Is the sequence [1,0] a subsequence of [A,B,C]? Where 1=married and 0=not.

[A,B,C] is either [1,1,0] or [1,0,0]. Both contain [1,0]. Yes.

edited Aug 22 '16 at 03:51

Jonathan Allan

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answered Aug 21 '16 at 04:32

J0S

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score 2 · Answer 7 · answered Aug 20 '16 at 07:40

The answer marked correct is correct to the spirit of the question. But since this is a puzzle, its fair to point out that there are cases where it might not be answerable.

This is a legal question and it requires that consistent laws apply to all participants to be unambiguously answerable. We don't know that's the case here.

Consider this scenario: Jack is in South Africa which recognizes his marriage and is looking at unmarried Anne who is standing a few feet away in Botswana where Jack's marriage is not recognized. In South Africa we have a married Jack looking at an unmarried Anne. As his gaze crosses the border the law changes and it becomes the gaze of an unmarried man on an unmarried woman.

You can keep the distracting gender/fidelity subtext and resolve the legal ambiguity by replacing "is married" with "is wearing a wedding ring".

I get your point here... but do look at the tags. it says 'logical deduction' not "lateral thinking" — Sid, Aug 20 '16 at 13:16
But... the definition of what a wedding ring is may vary between South Africa and Botswana, where the two are standing :-p Point is, if you want to nitpick, you're pretty much making it difficult to answer period. Define looking, define person... define is (temporal distortion anyone!?!) Once in a while a little straightforward logic is a beautiful thing (even if I did manage to get it wrong, humbling isn't so bad!) — JeopardyTempest, Aug 22 '16 at 07:40

score 0 · Answer 8 · answered Aug 20 '16 at 02:30

0

Jack(male, married) -> Anne(female, ?) -> George(male, unmarried). Where "->" means "is looking at"; "?" is one marital status among ("married" or "unmarried" or "civil partnership" or "married and then survived the spouse").

Anne is not determined, so it cannot be determined. If it were a Boolean problem, the answer would be "yes". However, real world problems are rarely binary.

answered Aug 20 '16 at 02:30

zyc

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Full marks for political correctness, but none for logic. Whatever other status they might have, everyone is either married or unmarried. Male or female makes no difference. – DJClayworth Aug 20 '16 at 04:06
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Agree with DJClayworth, except I'm not sure it's full marks for political correctness, either. The sexes of Jack, Anne, and George are not given, only their names. – Caleb Stanford Aug 21 '16 at 09:12

score -4 · Answer 9 · edited Aug 20 '16 at 01:29

-4

Answer: Yes. Because: George is the child of Jack and Anne. Married mother is looking at unmarried child.

edited Aug 20 '16 at 01:29

JMP

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answered Aug 20 '16 at 00:55

user29184

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This is not a lateral-thinking puzzle. What makes you think George is the child of the other two? – elias Aug 20 '16 at 01:27

Is a married person looking at an unmarried person?

9 Answers9