On Friday I posted this puzzle…..

The police know that either Dick, Jack, Sally, or Jimmy have stolen some money. Each suspects makes a statement, but only one of the statements is true.
Dick said, “I didn’t do it.”
Jack said, “Dick is lying.”
Sally said, “Jack is lying.”
Jimmy said, “Jack did it.”
Who committed the crime?
If you haven’t tried to solve the puzzle, have a go now.  For everyone else the answer is after the break.
Let’s suppose that Dick’s statement is true. Then, Jack’s is false, but Sally’s is true, which contradicts the notion that only one statement is true. So some other statement must be true, and therefore Dick’s is false. So, Dick committed the crime!
Did you solve it? How?
I have produced an ebook containing 101 of the previous Friday Puzzles! It is called PUZZLED and is available for the Kindle(UK here and USA here) and on the iBookstore (UK here in the USA here). You can try 101 of the puzzles for free here.

1. Roland says:

You have to evaluate the other options too. Luckily these turn out to be having more or less than one true statement.
And of course there’s always the option that Richard did it 😉

1. Jethro says:

I din’t think you do need to evaluate the other options. Within the ‘rules’ of the puzzle, only one person can be telling the truth. If logic identifies who that person is, or who can’t be that person and so is the culprit, then the puzzle is solved. It would be illogical to continue trying to find the answer to the puzzle.

2. Solved it this way, but did a “brute force” method afterwards to check if the puzzle was valid. And it was.

3. More or less the same way I figured it out. My process was this: All of the others focussed on Jack which meant they could not all be right (because only one statement was true). Therefore Jack was the only one of the remaining three who mentioned someone other than himself so Dick must have done it.

4. This was my first Friday puzzle, nice to have something to look at on a Monday morning, thanks,, I used the same approach but once I knew that dick was the crim I did not check the other possibilities and was happy to have him arrested 🙂

5. Jethro says:

It was slightly more obvious for me:
Jack and Sally’s comments are contradictory which means they can’t be both true or both false. As one of them must be true (irrelevant which) then all others must be false, including Dick’s statement that he didn’t do it.

However, to be horribly pedantic, you have to remember that there is a difference between a lie and an untruth. Lying requires intent to mislead. It could be that one or more of the statements are untrue but that the person who gave it believes it to be true in which case Sally and Jack’s statements don’t help and the puzzle is unsolvable 😉

1. Steve says:

Jestro. No need to apologise for being pedantic (assuming that’s what you were doing), It was a good point and adds an interesting dimension to it, for me anyway. I suppose that’s one of the ideas of these puzzles, to get us thinking perhaps beyond the initial statement. Steve.

2. Yes, this was my worry too. The puzzle would have been better stated in terms of truth and falsity (as the answer was).

3. Jefferson says:

Really? The beliefs of any of the characters is irrelevant. Their statements are either true or they are not. Whether they are deliberate lies or honest mistakes has no bearing on the solution.

What is of greater concern to me is why some of you care to nitpick over unimportant details and assign motives to the characters involved where none are either implied or required.

4. Steve says:

Jefferson. Some of us like to “nitpick” because it expands the discussion and perhaps leads to other or more interesting things. Keep you blinkers on if you wish but don’t get annoyed as us further discussing the puzzle.If you don’t like it then you know what to do.

5. Jethro says:

I wasn’t nit picking, I was being pedantic (if the smiley wasn’t enough to highlight to you the less than serious nature of my post then there is no hope for you)

However, I was also raising an interesting point about the nature of lying. Two of the characters stated that another is lying and the puzzle gives no wriggle room for the fact that someone may not have been lying yet their statement may also be untrue.

I recommend Sullyan’s ‘The lady or the tiger’ which has many more puzzles of this ilk, some of them contain Knaves (who always lie), knights (who always tell the truth), normals (who sometimes lie and sometimes tell the truth) and the insane (who either tell the truth but think they are lying or tell an untruth and think they are telling the truth). It’s books like that which influence the kind of critical thinking I’ve demonstrated above. Puzzles can be a lot more fun that way. Each to their own, I suppose.

6. Jeffrey says:

According to dictionary.com
1. Ostentatious in one’s learning
2. Overly concerned with minute details or formalisms, especially when teaching.

Nit picking

7. Steve says:

That’s the common definition but if a pedant or autistic person were to define pedantic then my guess is that it would less insulting and more meaningful as to the true reasons for its use. Being pedantic often leads to more detail and alternate explanations. Those that ‘accuse’ anyone of being pedantic are usually those that cannot see beyond the usual boundaries. They are limited in what they can see or detect. Their awareness is stunted. If the hat fits ,,,

6. Anne Elk says:

Really pleased that I got this one right! I kept doubting myself. I thought there would be something I’d missed.
Good puzzle!

7. dharmaruci says:

but do we know they each know who the killer is? what if sally is mistaken about jack and she lies about that?

8. Anonymous says:

I didn’t get it myself but it’s obvious when you think about it.

1. Why didn’t you think about it then?

9. Lazy T says:

It’s only modern police methods that produce such nice logic puzzles

10. zakir husain shaikh says:

Jack has stolen money

11. JeffJo says:

Alternate, slightly quicker, but just as valid solution: Only two statements say anything about who did it, Jimmy’s and Dick’s, so either Jack did it (as Jimmy claimed) or Dick did (as he denied). But if Jimmy is telling the truth, so is Dick. So Jack didn’t do it, and Dick did. A quick check shows that only Sally is telling the truth.

12. JeffJo, you should know not to trust Sally. Isn’t it obvious from the get go that Richard, I mean Dick, is the culprit?

1. JeffJo says:

I don’t trust Sally. It’s obvious everybody here lies, at least sometimes. But if Richard (not Dick) is to be trusted, one of these liars had to be telling the truth, and it can only be Sally. Unless Richard (or was it Dick?) wasn’t, in which case …. I did it.

13. Jack is telling the truth, not Sally.

14. I just worked through the four possibilities of who might have done it, and worked out how many statements were true in each case. I didn’t do the clever logic thing of working out how the statements cancelled each other out, or who was inside the gorilla suit.

But anyway, Jack and Sally’s statements both indicate that they have knowledge of what other suspects have said (in spite of the normal practice of witnesses’ statements being taken in isolation). Their statements must have been worked out in advance by collusion, which indicates a conspiracy. Under the principle of joint enterprise, at least three can be considered guilty.

15. Henry says:

My 9 year old and 11 year old both got it in about a minute. However, Richard did stump my 5 year old.

1. Steve says:

That does a lot for my ego … not ! 😉