# It’s the FridayPuzzle!

46

Please do NOT post your answer, but do say if you think you have solved the puzzle and how long it took. Solution on Monday.

There are four suspects, and one of them has committed a murder.  They make the following statements, but only one of them is telling the truth.  Who committed the murder?

Jon: James did it.
James: Bob did it.
Sid: I didn’t do it.
Bob: James is lying.

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.

## 46 comments on “It’s the FridayPuzzle!”

1. Chris says:

3. Anne Elk says:

We had a puzzle like this a few months ago and I still can’t do it! Memory like a sieve.

4. Alma says:

About 2 minutes. Seemed fairly easy so I must have got it wrong. 🙂

5. Louise says:

6. Eddie says:

Can’t do this sort of puzzle but have an answer based on probability.

• Eddie says:

PS Hi Charlie!

7. ChrisR says:

Yes, I’m sure we’ve had something like this recently.
But for me it was 45 seconds to get an answer, then another 4 minutes exploring other ways of solving it only to realise my answer was wrong and then another minute to get what I think now is the right one

8. Skatz says:

I love these logic puzzles. Took me about 3 mins but I’ve only had 4 hours sleep. It’s possible to get it from what only 2 of them are saying, if you pick the right 2. Can’t say more without revealing the answer

• ChrisR says:

I thought that initially, but I’m not so sure now. Will re-ponder over lunch and then wait until Monday

• Kevin says:

You might as well say more, because you’re wrong.

• Slow Learner says:

I’m with Kevin here, Skatz.
If you just look at two people’s statements the options are:-
Both are lying
Both are telling the truth
One is lying and one is telling the truth.
From the above how do you manage to ascertain whether the other two people are telling the truth?
Please let us now how you have done this on Monday – we don’t want any spoilers do we?

• ChrisR says:

Repondered – happy with my second answer and agree with kevin

• Anders says:

You also need the premise that only one of them is telling the truth as well as an assumption of what it means to tell the truth. as far sd I can tell Sid is the only ony one where honesty and accuracy are synonyms since presumably he knows what he did all the rest can be truthful and just plain wrong anonymous you know you’re right when the ghost of the victimstarts haubting one of them, just sit back and wait for the broken glasses Edwards who really did it – yes I have been watching too much supernatural

• Yat says:

If you know that among two people, exactly one is telling the truth (one statement is enough to know that), then the other two lie. From then on there is a statement that allows to know who did it.
So Skatz is right, you need only two of the statements.

• Slow Learner says:

Thanks Anders and Yat.

So your logic, Anders, is that because Sid “knows what he did” he is telling the truth. Is this a general solution for all puzzles of this nature?

Yat, you state that “If you know that among two people, exactly one is telling the truth (one statement is enough to know that), then the other two lie”. Doesn’t that make three people?

9. Anonymous says:

10. mgm75 says:

Yes, I’m pretty sure we had this one just a few weeks ago. Figured it out quickly then and same again.

11. ctj says:

one minute to get a solution; another to confirm that it is unique.

12. Stan says:

about 4 min. It was fun.

13. Anonymous says:

got

14. Steve Jones says:

Of course this is all rather perverse in that the answer is based on most of the suspects lying. As the police can’t possibly know just one suspect is telling the truth, then things don’t look to good for one suspect as he’s been fingered as the murderer by one suspect, as a liar by a second and this is consistent with the reply of the third and he has every motive to lie about his role.

Given this, he would be the most likely person to be convicted. As it is, the answer will be the person least likely to have committed the act on the basis of the evidence. In the case of the “right answer”, there’s no obvious personal protection motive for two of the lies (of course, you can’t rule out friend/enemy relationships between the suspects).

• Nonny Mouse says:

Slow day, Steve? 🙂

• ctj says:

that’s the thing that bugs me about logic problems like this – the premise is so illogical.

15. Lazy T says:

I did it, with a pencil in the kitchen.
2 mins. and I liked it.

16. Whistler says:

Yes you did! 🙂

17. mittfh says:

Took a couple of minutes – started off by working out who each suspect claimed did / did not do it, then a couple of steps later (work ’em out for yourselves!) was presented with only one scenario which could meet the puzzle requirements.

18. Anonymous says:

a few minutes

19. Ratt Mutter says:

2 minutes!!!!

20. ross says:

didn’t you put this one out ages ago?

21. Pat Harkin says:

Well, obviously I worked out who did it immediately, but first I needed to resolve some unfinished business with my ex, get back at the by-the-book superintendent and explore the sexual tension with my new DI. All of which will be forgotten by the time next week’s puzzle starts.

22. jokkiboy says:

2 minutes…

23. wharton147 says:

Working this out looks like a lot of trouble. Perhaps it’ll be easiest if we just beat a confession out of one of these guys. The main thing here is to keep the statistics looking good.

24. dayuntoday says:

Between 3-4 minutes. First time through, I came up with impossibilities for all of them. Tough, but fun!

25. About 2 minutes. I checked how many true statements there would have been if each of the four suspects did it, and only one possibility yielded 1 true statement and 3 lies.

As usual, I thought about the puzzle and wrote my comment *BEFORE* reading the comments in the thread; I am now going to go and read the thread to see how many moans and whinges there are about spoilers, due to the fact that some people seem to insist on reading the thread first despite knowing that it is likely to contain spoilers.

• Anon says:

In that you have stated a methodology which yields the answer, doesn’t your post constitute a spoiler LoonMeister?

26. Gene says:

less then a minute

27. Tim Jones says:

Richard did it.

28. tuftychain says:

Sid did it…!!!

29. akaura says:

1 min

30. Uber says:

Solved in 3 minutes. One for finding the solution, and two more minutes for being sure…

31. shiningsteve says:

About 5-10 minutes – I had to get a pen and paper and make some notes to be sure.

32. Em Hall says:

One minute erm…..I got it……I think……