Bonnie bought a bag of birdseed. She left it in her apartment (#5) before she went to work, intending to fill the feeder that afternoon. But when she got back, the bag of birdseed was gone!

  There were four other people living in the same apartment building as her, all of whom were avid birdwatchers like Bonnie. One of them must have done it. Look at the clues below. If you know everybody's name, apartment number (#1 through #4), and favourite bird, you will know who is guilty.

1. The guilty person's apartment number is not numbered one higher or one lower than Hal's.
2. Joe's favourite bird is the crow; his apartment number is one lower than that of Ike (who doesn't like robins).
3. The guilty person's apartment is not #3 (the number of the finch-lover's).
4. Gil is neither at apartment #1 nor the wren-lover.

Whodunit?

Normally, I don't particularly like these grid puzzles much, but the good response to this one compelled me to take a look.  I only read enough of the comments to know how to interpret "If you know everybody's name, apartment number (#1 through #4), and favourite bird, you will know who is guilty," correctly.

Now, a full explanation.

Notice that there are only two clues about the guilty person's identity.  We know he is not at #3, and not at a number one higher or one lower than Hal's number.  The only way we can know who the guilty is if Hal is in #3.  The guilty person must be in #1.

We know Gil isn't in #1 from clue 4.  We know Ike isn't in #1 from clue 2 because Joe has a lower number.  Hal is in #3, not #1.  So naturally, Joe must be the guilty person.  Problem solved.  Nothing more must be done.

Of course, I worked out the whole thing on paper before realizing the reasoning two paragraphs above.  Strangely enough, I couldn't tell who was in apartments #2 and #4 even afterwards.

Edit:  Ah... I see.  Clue 2 says Joe is *one* lower than Ike.  I had missed that.

Edited on November 6, 2004, 5:14 pm

Posted by Tristan on 2004-10-30 14:46:23