Avery , Blake , Clark and Doyle each live in an apartment. Their apartment are arranged like this :
| A | B | C | D | --> East
- One of the four is the landlord.
- If Clark's apartment is not next to Blake's apartment, then the landlord is Avery & lives in apartment A.
- If Avery's apartment is east of Clark's apartment, then the landlord is Doyle and lives in apartment D.
- If Blake's apartment is not next to Doyle's apartment, then the landlord is Clark and lives in apartment C.
- If Doyle's apartment is east of Avery's apartment, then the landlord is Blake and lives in apartment B.
Who is the landlord?
(In reply to explaining my approach
by Ady TZIDON)
One quibble with your approach. There is no guarantee that the landlord actually lives in his corresponding apartment In other words, the solution does not need to be Axxx or xBxx or xxCx or xxxD. All other things being equal, the probability is only 25% that the landlord lives in his corresponding apartment. Looking at statement 2, for instance, it is possible that Blake lives next to Clark, Avery is the landlord, but Avery lives in B or C or D. In other words, there are 16 initial guesses, including xAxx. So yes, I would say that you were very lucky with your initial guess.
I rate this excellent problem a difficulty 3 (or 2 if pushed to compromise). Compare it, for instance, to the just published "Musket Mettle", which is rated difficulty 3 even though it is much easier to prove that Musket Mettle has only one solution.
Edited on February 8, 2013, 2:06 pm