PUZZLE : The Case of Honest Suspects

Handel has been killed and Beethoven is on the case. 

He has interviewed the four suspects and their statements are shown below. Each suspect has said two sentences. One sentence of each suspect is a lie and one sentence is the truth. 

Help Beethoven figure out who the killer is.

Joplin: I did not kill Handel. Either Grieg is the killer or none of us is.

Grieg: I did not kill Handel. Gershwin is the killer.

Strauss: I did not kill Handel. Grieg is lying when he says Gershwin is the killer.

Gershwin: I did not kill Handel. If Joplin did not kill him, then Grieg did.

Click here to know who is the killer! 

DETECTION : Killer in The Case of Honest Suspects

What was the case?

Let's first see what are the statements made by 4 suspects.

Joplin: I did not kill Handel. Either Grieg is the killer or none of us is.

Grieg: I did not kill Handel. Gershwin is the killer.

Strauss: I did not kill Handel. Grieg is lying when he says Gershwin is the killer.

Gershwin: I did not kill Handel. If Joplin did not kill him, then Grieg did. 

ANALYSIS :

1] If Joplin is the killer then his first statement would be lie & other statement must be true. But his second statement contradicts assumption that he is killer. So Joplin can't be the killer.

2] Let's assume Grieg is the killer. His first statement must be lie and second must be true. His second statement points to Gershwin as a killer. But there is one killer among 4 so Grieg and Gershwin can't be killers together. Therefore, Grieg can't be the killer.

3] Suppose Gershwin is the killer. Again, his first statement is lie and second is true. His true second statement suggests that Grieg is the killer as Joplin is assumed to be innocent in the case. Again, both Grieg and Gershwin can't be killers together since there is only one killer. Hence, Gershwin is not the killer.

4] Therefore, Strauss must be the killer. His first statement is lie and second statement is true. And that's how Grieg is lying when he is saying Gershwin is the killer.

CONCLUSION : 

STRAUSS is the one who committed the crime and his first statement is lie and second is true.

The first statements of rest of all suspects are true and second statements of each are lie.  

 

Who is the President of Logitopia?

Larry, Matt, and Nick live in the strange country of Logitopia. 

This country is inhabited by three races of people: the type A people who always tell the truth, the type B people who always lie, and the type C people who alternately tell the truth and lie. One of the three is the president of Logitopia.

Larry makes these two statements:

1. "The president is of a different race from the other two."
2. "Matt is not the president."

Matt makes these two statements:

1. "The president is a type B person."
2. "Larry is not the president."

Nick makes these two statements:

1. "Exactly two of us are of the same race."
2. "I am not the president."

Who is the president?

Know the NAME of the President!
 

Larry is the President of Logitopia

What was the puzzle?

First thing to note that it's not mentioned any where that three people are three different types; there may be 2 who are the same type.

Let's have a look at the statements made by 3.

Larry makes these two statements:

1. "The president is of a different race from the other two."
2. "Matt is not the president."

Matt makes these two statements:

1. "The president is a type B person."
2. "Larry is not the president."

Nick makes these two statements:

1. "Exactly two of us are of the same race."
2. "I am not the president."
  
We'll refer Larry's statements as L1 & L2, Matt's as M1 & M2 and those of Nick's as N1 & N2.

ANALYSIS : 

1] Suppose Matt's first statement M1 is TRUE. So, he is not a TYPE B person for sure & hence not the president. Therefore, L2 must be TRUE making sure Larry is not TYPE B person nor a president. So, Nick must be the president & TYPE B person whose both statements are FALSE. Since, N1 is turning out to be FALSE, neither Matt nor Larry can be TYPE B or both of them can't be of the same type i.e. TYPE A or TYPE C. 

However, since M2 turns out to be TRUE, Matt must be TYPE A person and hence leaving Larry as a TYPE C person. In that case, since L2 is TRUE, L1 must be FALSE. But in the case the president (TYPE B) is really different from the other two (TYPE A and TYPE C) making L1 TRUE. So, the assumption that M1 is TRUE goes wrong here in the case.

2] Now, let's suppose that Matt himself is the president. Then, L2 must be FALSE and M2, N2 would be TRUE. Since, M2 is TRUE, Matt (the president) can't be TYPE B & we know M1 is FALSE,  Matt must be TYPE C person & president.

Anyhow, Larry's first statement L1 can't be TRUE as in that case, he too will be TYPE C person as president Matt which is against the statement L1 itself. Since, his other statement L2 is FALSE, he must be TYPE B person.

Now, with N2 to be TRUE, if N1 is assumed to be TRUE then Nick would be TYPE A person. So, all three would belong to 3 different races which contradicts statement N1 itself. Hence, N1 must be FALSE. 

And if N1 FALSE and N2 TRUE, Nick would be TYPE C person as president Matt while Larry being TYPE B person. But this makes statement N1 TRUE which again contradicts our conclusion above. 

Therefore, Matt too can't be the president.

3] Suppose Nick is the president. That would make N2 FALSE and L2, M2 TRUE.
As concluded in STEP 1 above, we know M1 has to be FALSE. Then the President Nick can't be TYPE B person. With one of his false statement N2, Nick must be TYPE C person. Therefore, N1 must be TRUE. So, both Matt and Nick are TYPE C persons. 

That indicates president isn't of a different race than other two. That is L1 turns out to be FALSE. With L2 proved TRUE already, Larry would be TYPE C person. So all three would be TYPE C which contradicts TRUE statement N1.

4] Therefore, Larry must be the president.

That is L2, N2 must be TRUE and M2 must be FALSE. With M1 proved FALSE already in [1] above, Matt must be TYPE B person. Nick can't be TYPE B person with TRUE N2. 

If N1 is TRUE (i.e. Nick is TYPE A person) then Larry must be the other person with TYPE A (since Matt is TYPE B person) along with Nick for N1 to be TRUE. So, L1 too has to be TRUE. But, the president Larry is of the same race as that of Nick which is against L1 itself.

Hence, N1 must be FALSE and Nick must be TYPE C person. And therefore, L1 has to be TRUE making president Larry as a TYPE A person.

CONCLUSION : 

The President of Logitopia is Larry who is TYPE A person. Matt is TYPE B person and Nick is TYPE C person. 

Black or White Dot on Forehead

There are five men, let's say Tarun, Harish, Lavesh, Manoj and Manish. All of them have a dot mark in their forehead. They can't see the dot on their own forehead, but can see the ones on others. The owner of WHITE dot is an honest person and will never lie, while the owner of BLACK dot always tell the lie.

This are the statement from Tarun, Harish, Lavesh, and Manish:

Tarun: 'I see 3 whites and 1 black'

Harish: 'I see 4 black'

Lavesh: 'I see 3 black and 1 white'

Manish: 'I see 4 white'

What color is the dot on each Tarun, Harish, Lavesh, Manoj, Manish forehead?

Know color of dot on each forehead!

Source 

Men with White Dots on Foreheads

Read this story first!

Let's take a look at who said what. 

Tarun: 'I see 3 whites and 1 black'
Harish: 'I see 4 black'
Lavesh: 'I see 3 black and 1 white'
Manish: 'I see 4 white'
 
Harish and Manish made very contracting statements; so are statement of Tarun and Lavesh. That means, only one of them is telling the truth. Hence, only one of 4 have WHITE dot on his forehead. Till now we don't have idea of what Manoj had on his forehead. Even if he has WHITE dot then there can be maximum 2 WHITE dots among those 5.    

Truth of Tarun and Manish:

Tarun and Manish must be lying as they are saying that they have seen 3 and 4 WHITE dots respectively. According to our first conclusion, there can be maximum 2 WHITE dots possible.

Truth of Harish:

Next if we assume Harish has WHITE dot and telling the truth then all other must be lying including Manoj and Lavesh. As per Lavesh, he had seen 3 BLACK and 1 WHITE dot. Now he must have seen BLACK dots on foreheads of Manoj, Tarun, Manish and WHITE dot on forehead of Harish as assumed. That mean he is telling truth though he has BLACK dot. But the man with BLACK is always lying, hence this case is also INVALID. 

Truth of Lavesh:

So the only person left is Lavesh and must be telling the TRUTH with WHITE dot on his forehead. Hence, as his statement is suggesting, the Manoj must have WHITE dot and other three Tarun, Lavesh, Harish have BLACK dots (we already concluded these 3 are lying).