Logic Puzzles Marathon (1 Viewer)

[Paradoxica]

White to move, mate in 6. Orientation is towards white, as per usual.
Multiple solutions exist. Good luck.

 

[Paradoxica]

 

[leehuan]

The answer to the above qn was 2, 1, 0 because it was actually inclusive of the answer itself.
______________________________

"Watson, I have uncovered the following facts:

- If Mrs Smith is lying then Moriarty has not escaped.
- Either Moriarty is dead or he is really Jones
- If Moriarty is really Jones then he has escaped.
- I am convinced Mrs Smith is lying."

"Good Lord Holmes," replied Dr Watson, "what can you make of all this?"
"Elementary my dear Watson, Moriarty is dead!"

Prove that Sherlock is as always, correct.

This is a randomly chosen question from my homework. It isn't intended to be hard if you know what you're doing, but if you don't then it can be hard.

 

[Orthos]

Mrs Smith is lying, so Moriarty has not escaped which means Moriarty is not Jones. Lastly, Moriarty is either dead or is Jones and we know that Moriarty is not Jones which allows us to conclude that Moriarty is dead!

Hard part was concluding Moriarty is not Jones given that Moriarty has not escaped.

 

[Paradoxica]

Mrs Smith is lying, so Moriarty has not escaped which means Moriarty is not Jones. Lastly, Moriarty is either dead or is Jones and we know that Moriarty is not Jones which allows us to conclude that Moriarty is dead!

Hard part was concluding Moriarty is not Jones given that Moriarty has not escaped.

That's not quite correct. The IF statements only work one way. They are not bijective implications. For that to be so, they would have to be IFF statements.

 

[leehuan]

l

therefore ~m

therefore ~j

therefore d



I don't see a mistake in Orthos' sentences.

 

[Drsoccerball]

The answer to the above qn was 2, 1, 0 because it was actually inclusive of the answer itself.
______________________________

"Watson, I have uncovered the following facts:

- If Mrs Smith is lying then Moriarty has not escaped.
- Either Moriarty is dead or he is really Jones
- If Moriarty is really Jones then he has escaped.
- I am convinced Mrs Smith is lying."

"Good Lord Holmes," replied Dr Watson, "what can you make of all this?"
"Elementary my dear Watson, Moriarty is dead!"

Prove that Sherlock is as always, correct.

This is a randomly chosen question from my homework. It isn't intended to be hard if you know what you're doing, but if you don't then it can be hard.

l = Mrs Smith is lying
e = Moriarty has escaped
d = Dead
j = He is Jones
----------------------------------------
l -> ~e (1)
d V j (2)
j -> e (3)
l (4)
---------------------------
l (4)
~e (1)
~j (3)
d (4) (Since not j)
[]

EDIT: nvm you got it.

 

[Orthos]

That's not quite correct. The IF statements only work one way. They are not bijective implications. For that to be so, they would have to be IFF statements.

See #modustollens on statement 3 of the question.

 

[Orthos]

What do you think is the fastest way to do that type of "mystery puzzle" in real life? Or if you were playing detective. Practice and think in formal logic? Practice deductive reasoning and use common sense? Something else?

 

[leehuan]

Symbols made life easier for me after I learnt how to do those.

But if you can practice to be quicker at deductive reasoning (with common sense if necessary), sure.