Please Help With Clue

[ljspivey]

I keep getting this type of clue in various puzzles and I cannot make it make since. Can someone help?

"If Alfonso is either Front Reef or 18, and Front Reef does not equal a different item in the same category as 18 (in this case, 21), then Alfonso cannot equal 21. Mark the highlighted cell as FALSE. (+120 sec. penalty)"

[Alethea]

I hope my explanation will help. So Alfonso either has to be on 18 or on Front Reef. If he is not on 18 - that is, if he is on any other number - then he must be on Front Reef. Any number, then, that Front Reef can't be, he can't be on either (18 is the only exception). So if Front Reef can't be 21, Alfonso can't be 21. If Alfonso were 21, he wouldn't be 18, and if he's not 18, he must be on Front Reef. Those are his only two choices - either 18 or Front Reef. If he's not on 18, then everything about him has to match up with everything about Front Reef, because that's where he is.

[stiffethaman]

I hope my explanation will help. So Alfonso either has to be on 18 or on Front Reef. If he is not on 18 - that is, if he is on any other number - then he must be on Front Reef. Any number, then, that Front Reef can't be, he can't be on either (18 is the only exception). So if Front Reef can't be 21, Alfonso can't be 21. If Alfonso were 21, he wouldn't be 18, and if he's not 18, he must be on Front Reef. Those are his only two choices - either 18 or Front Reef. If he's not on 18, then everything about him has to match up with everything about Front Reef, because that's where he is.

Not sure if I understood the question correctly, but I think "If Alfonso is either Front Reef or 18" means that IF Alfonso is either of those, then Front Reef (something), then Alfonso cannot equal 21. So I don't think Alfonso has to be 18 or Front Reef, but I might have misinterpreted it.


ljspivey. Can you maybe provide the entire puzzle? That will probably make it easier to provide an explanation.

[iluvrobin13]

I think the hint should say "since" instead of "if" he is. One of the clues should tell you that Alfonso IS either 18 or Front Reef.

[boxeeboxeebox]

If I'm remembering the puzzle correctly, the puzzle's variables are: dive date, dive instructor, dive customer, and dive location. I've mocked up a smaller version with just the variables mentioned in the original post, using mock names/dates.
The hint is based on two clues:

1. Alfonso either went to Front Reef or dived on April 18
2. Front Reef was not a dive location on April 21.

From 1, you can cross out April 18 from the Front Reef column.
From 2, you can cross out April 21 from the Front Reef column.
Going back to 1, consider the dates that Alfonso went diving:

• If Alfonso went diving on April 18, that's straightforward:
  • The result is a checkmark on April 18 and all other date boxes for Alfonso is crossed out.
• If Alfonso didn't go diving on April 18, then he must have gone to Front Reef.
  • If he went to Front Reef, then he would not have gone diving on either April 18 or April 21.
  • The result is no checkmark*, but April 18 and April 21 are crossed out. (*in the date column, but there is a checkmark for the intersection of Alfonso and Front Reef)

Note that in both cases above, April 21 would be crossed out. This is what the hint is telling you.

There's actually a pretty detailed tutorial on this site for all the tricks you can use to solve puzzles:
https://logic.puzzlebaron.com/how-to...gic-puzzle.php

For this specific case, you'll want to look at:
Either/Or Clues
https://logic.puzzlebaron.com/how-to...ither-or-clues
Transitive Relationships (Either/or)
https://logic.puzzlebaron.com/how-to...hips-either-or
Unaligned Pair Clues
https://logic.puzzlebaron.com/how-to...ned-pair-clues

They all have clear, step-by-step diagrams, so even if you don't quite understand the reasoning behind it, you can still apply the technique via visual inspection.