Jump to content


Welcome to BrainDen.com - Brain Teasers Forum

Welcome to BrainDen.com - Brain Teasers Forum. Like most online communities you must register to post in our community, but don't worry this is a simple free process. To be a part of BrainDen Forums you may create a new account or sign in if you already have an account.
As a member you could start new topics, reply to others, subscribe to topics/forums to get automatic updates, get your own profile and make new friends.

Of course, you can also enjoy our collection of amazing optical illusions and cool math games.

If you like our site, you may support us by simply clicking Google "+1" or Facebook "Like" buttons at the top.
If you have a website, we would appreciate a little link to BrainDen.

Thanks and enjoy the Den :-)
Guest Message by DevFuse
 

Photo
- - - - -

3 Princess Puzzle


  • Please log in to reply
11 replies to this topic

#11 Guest_Colinhead_*

Guest_Colinhead_*
  • Guests

Posted 06 January 2008 - 08:20 PM

Here are four questions that work.
Select the least desirable Princess and call her A.

[1] is B older than C?
[2] does B lie less frequently than C?
[3] is B more likely to lie than you?
[4] if I were to ask, would you say that B is Princess Mischievous?

In each case, if the answer is Yes choose C; if No, choose B.

Princess Truth and Princess Lie will answer Yes if Princess C is the other of these two, and No if Princess B is.
If A is Princess Mischievous, a random B or C choice gets you a winner either way.


I see how 1 and 2 work (because they are basically the same as OP's answers.),

but I don't think 3 or 4 work.

3)

Okay, so if I ask Honest (A) if B is more likely to lie than her, she says yes. But, she says yes whether B is Mischievous or Liar, so I may end up with Mischievous, never mind the fact that I don't know that A is honest.

The case is the same with Liar. She will say yes to either one so there is no way to distinguish between them.

So basically, if you ask the question of Liar or Honest, you have a 50% chance.

4)

Okay, so I ask A if B is Mischievous. She says yes. I don't know whether A is Honest or Liar (or Misch but that point is moot since you're a winner either way if you ask her), so do I pick B or C?

So, again, my future lies on chance. Not cool.
  • 0

#12 bonanova

bonanova

    bonanova

  • Moderator
  • PipPipPipPip
  • 5918 posts
  • Gender:Male
  • Location:New York

Posted 08 January 2008 - 07:23 PM

I don't think 3 or 4 work.

3) Okay, so if I ask Honest (A) if B is more likely to lie than her, she says yes.
But, she says yes whether B is Mischievous or Liar, so I may end up with Mischievous,
never mind the fact that I don't know that A is honest.

The case is the same with Liar.
She will say yes to either one so there is no way to distinguish between them.

So basically, if you ask the question of Liar or Honest, you have a 50% chance.

You're right - [3] is a broken version of [2].
I had something else in mind. Good catch.
.

4) Okay, so I ask A if B is Mischievous. She says yes.
I don't know whether A is Honest or Liar (or Misch but that point is moot since you're a winner either way if you ask her), so do I pick B or C?

So, again, my future lies on chance. Not cool.

Actually, [4] works. Remember, I said ...
In each case, if the answer is Yes choose C; if No, choose B.
PT and PL will both reliably identify PM.
If A is PT, she tells the truth about telling the truth, and if A ls PL, she lies about lying.


  • 0
The greatest challenge to any thinker is stating the problem in a way that will allow a solution.
- Bertrand Russell




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users