All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars    
perplexus dot info

Home > Logic
Day-knights and night-knights 4 (Posted on 2012-07-02) Difficulty: 2 of 5
There is a land where every inhabitant is either a day-knight or a night-knight. Day-knights tell the truth in the day and lie at night. Night-knights lie in the day and tell the truth at night. An inhabitant says, "Either I am a day-knight or it is day." Is the inhabitant a day-knight or a night-knight, and is it day or night?

See The Solution Submitted by Math Man    
Rating: 3.0000 (1 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Solution Solution (including what "or" is meant) Comment 2 of 2 |
There are four choices. Either inhabitant is:

1) A day-knight at day (tells truth).
2) A day-knight at night (tells lie).
3) A night-knight at day (tells lie).
4) A night-knight at night (tells truth).

If the "either __ or __" statement's "or" is exclusive, it works the following way:

Either T or T = F
Either T or F = T
Either F or T = T
Either F or F = F

1) Cannot be the answer since as a day-knight (T) at day (T), statement is false (but day-knight should be truthful).
2) Cannot be the answer since as a day-knight (T) at night (F), statement is true (but day-knight should be lying).
3) Cannot be the answer since as night-knight (F) at day (T), statement is true (but night-knight should be lying).
4) Cannot be the answer since as a night-knight (F) at night (F), statement is false (but night-knight should be truthful).

Given that none can be the answer, we have to assume the "or" is inclusive, so:

Either T or T = T

So, 1) is the solution. Day-knight in the day.

  Posted by Monika on 2012-08-11 20:00:50
Please log in:
Login:
Password:
Remember me:
Sign up! | Forgot password


Search:
Search body:
Forums (0)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (8)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Chatterbox:
Copyright © 2002 - 2024 by Animus Pactum Consulting. All rights reserved. Privacy Information