Binary Logic Practice Questions : Level 01

DIRECTIONS for questions 1 to 3: Select the correct alternative from the given choices.
  1. Bholu Prashad, Dholu Prashad and Golu Prashad participated in a quiz contest and each one of them received exactly one position amongst the Senior Manager, Manager, and Assistant Manager. When asked, "Who among you three is the senior manager?", following were their replies:
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Bholu Prashad: I am the Senior Manager.
Dholu Prashad is not the Manager.
Dholu Prashad: I am the Senior Manager,
Bholu Prashad is the Assistant Manager.
Golu Prashad: I am the Senior Manager.
Dholu Prashad is the Assistant Manager.
It is also known that one among them always tells the truth, one always lies and one alternates between the truth and lie (not necessarily in that order).
Who can never be the manager?
1. Bholu Prashad
2. Dholu Prashad
3. Golu Prashad
4. Cannot be determined
Sol: Option: 2
Explanation: (T ® True; F ® False)
(i) Assuming that Bholu Prashad is the Truth-teller, we get the following arrangement:
  Statement I Statement II    
Bholu Prashad T T Truth teller Senior Manager
Dholu Prashad F F Liar Assistant manager
Golu Prashad F F Alt. manager
(ii) Assuming Dholu Prashad is the Truth-teller, we get the following arrangement:
  Statement I Statement II    
Bholu Prashad F T Alt. Assistant Manager
Dholu Prashad T T Truth teller Senior Manager
Golu Prashad F F Liar Manager
(iii) Assuming Golu Prashad is the Truth-teller, we get the following arrangement:
  Statement I Statement II    
Bholu Prashad F T Alt. Manager
Dholu Prashad F F Liar Assistant Manager
Golu Prashad T T Truth-teller Senior Manager
Hence, either Bholu Prashad or Golu Prashad can be the Manager, but not Dholu Prashad.
  1. Each person out of X, Y and Z had exactly one different title amongst the Fast, the Slow and the Beautiful. Also, each person always gave two replies to any question. Exactly one among them always spoke the truth, another always lied and the last person always alternates between truth and lie (in any order). When asked about their titles, the following were their replies:
X:
Y is 'the Fast'.
I am 'the Beautiful'.
Y:
Z is 'the Slow'.
X is not 'the Fast '.
Z:
Y is 'the Beautiful'.
X is not 'the Slow'.
Which among the following choices has the names of the persons who had the title the Fast, the slow and the beautiful respectively?
1. X, Y, Z
2. Z, X, Y
3. Y,Z, X
4. X, Z, Y
Sol: Option: 4
Explanation: If X always speaks the truth, then Y Is the Fast', X is the Beautiful', hence z is 'the slow'; which also means that Y is also the truth-teller. Hence, neither X nor Y is the truth-teller.
Therefore, Z must be the truth-teller, which gives us the following arrangement:
X → the Fast;
Y → the Beautiful;
Z → the Slow
Hence, Z is the Slow.
  1. John, Johny and Janardan participated in a race and each won a different medal among Gold, Silver and Bronze, not necessarily in that order. Each person among them gives two replies to any question, one of which is true and the other is false (in any order). When asked about the details of the medals obtained by them, the following were their replies:
John:
I won the Gold medal.
Johny won the Bronze medal
Johny:
John won the Silver medal.
I won the Gold medal.
Janardan:
Johny won the Silver medal.
I won the Gold medal.
Which among the following is the correct order of the persons who won the Gold medal, the Silver medal and the Bronze medal respectively?
1. John, Johny, Janardan
2. Janardan, John, Johny
3. Johny, Janardan, John
4. Janardan, Johny, John
Sol: Option: 2
Explanation: Each among John, Johny and Janardan is an Alternator.
Let John's first statement be true and second be false;
  I II Medal
John T F Gold
Johny F F Silver
Janardan T F Bronze
Hence, Johny is not an Alternator, which means our initial assumption was false.
Let John's first statement be false and second be true:
  I II Medal
John F T Silver
Johny T F Bronze
Janardan F T Gold
Hence, Janardan ⇒ Gold medal
John ⇒ Silver medal
Johny ⇒ Bronze medal
DIRECTIONS for questions 4 to 6: These questions are based on the following information.
Each of the three persons – Sham Lal, Ram Lal and Mohan Lal-belonged to exactly one of different cities amongst Ambala, Karnal and Panchkula. Each person always gives two replies to any question asked. Out of these three, exactly one person always speaks the truth, other always lies and the another always alternates between truth and lie, in any order. When each was asked "Which city do you belong to?", the following were their replies:
Sham Lal: I am from Ambala. Ram Lal is from Karnal.
Ram Lal: I am from Ambala. Mohan Lal is from Panchkula.
Mohan Lal:Sham Lal is from Karnal. Ram Lal is from Ambala.
Based on the above, Sol the following questions:
  1. Who among the three must be from Panchkula?
1.Sham Lal
2. Ram Lal
3. Mohan Lal
4. Cannot be determined
Option: 3
Explanation: (i) Assuming Sham Lal always speaks the truth:
  I II City
Sham Lal T T Ambala
Ram Lal F T Karnal
Mohan Lal F F Panchkula
(ii) Assuming Ram Lal always speaks the truth:
  I II City
Sham Lal F F Karnal
Ram Lal T T Ambala
Mohan Lal T T Panchkula
(iii) Assuming Mohan Lal always speaks the truth:
  I II City
Sham Lal F F Karnal
Ram Lal T T Ambala
Mohan Lal T T Panchkula
From all three situations , it is concluded that Mohan Lal must be from Panchkula.
  1. Which city did Ram Lal belong to?
1. Ambala
2. Karnal
3. Panchkula
4. Panchkula or Ambala
Option: 2
Explanation:
(i) Assuming Sham Lal always speaks the truth:
  I II City
Sham Lal T T Ambala
Ram Lal F T Karnal
Mohan Lal F F Panchkula
(ii) Assuming Ram Lal always speaks the truth:
  I II City
Sham Lal F F Karnal
Ram Lal T T Ambala
Mohan Lal T T Panchkula
(iii) Assuming  Mohan Lal always speaks the truth:
  I II City
Sham Lal F F Karnal
Ram Lal T T Ambala
Mohan Lal T T Panchkula
From the above situations, it is concluded that Ram Lal belongs to Karnal.
  1. If there are exactly two persons who always tell the truth and the third person either always lies or alternates between truth and lie, then which of the following statements must be false?
1. Mohan Lal is not from Karnal
2. Sham Lal is not from Ambala.
3. Mohan Lal is not from Panchkula.
4. Ram Lal is from Ambala
Option: 3
Explanation:
(i) Assuming Sham Lal always speaks the truth:
  I II City
Sham Lal T T Ambala
Ram Lal F T Karnal
Mohan Lal F F Panchkula
(ii) Assuming Ram Lal always speaks the truth:
  I II City
Sham Lal F F Karnal
Ram Lal T T Ambala
Mohan Lal T T Panchkula
(iii) Assuming  Mohan Lal always speaks the truth:
  I II City
Sham Lal F F Karnal
Ram Lal T T Ambala
Mohan Lal T T Panchkula
Hence, Mohan Lal is not from Panchkula is false.
DIRECTIONS for questions 7 to 9: These questions are based on the following information.
There are four persons - A, B, C and D - each of whom plays exactly one game from amongst Cricket, Football, Table-Tennis and Tennis. No game is played by two persons. Each person gives two replies to any question asked to them. At least one person among them always speaks the truth and at least one person always tells lies. There is at least one person who always alternates between the truth and lie in any order.
When asked about the names of the persons and the respective games played by them, following were their replies:
A : I play Cricket. C plays Cricket.
B : I play Tennis. D plays Tennis.
C : A plays Table-Tennis. B plays Cricket.
D : C plays Football. I play Table-Tennis.
It is also known that D plays Tennis and a definite arrangement can be obtained from the statements given by each person.
  1. Who among the following plays Cricket?
1. A
2. B
3. C
4. D
Option: 2
Explanation: It is known that D plays Tennis, which means that the 2nd statement made by B must be true, whereas the 2nd statement made by D must be false. As A says that he and C both play cricket, A cannot be the person who always speaks the truth, as each person plays exactly one game and exactly one game is played by each person. This means only C can always speak the truth, as there must be at least one person who always speaks the truth.
We take this as the basis and get the arrangement as given below:
  I II Game played
A F F Table-tennis
B F T Cricket
C T T Football
D T F Tennis
Hence, B plays Cricket.
  1. Who among the following always speaks the truth?
1. A
2. B
3. C
4. D
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Option: 3
Explanation: It is known that D plays Tennis, which means that the 2nd statement made by B must be true, whereas the 2nd statement made by D must be false. As A says that he and C both play cricket, A cannot be the person who always speaks the truth, as each person plays exactly one game and exactly one game is played by each person. This means only C can always speak the truth, as there must be at least one person who always speaks the truth.
We take this as the basis and get the arrangement as given below:
  I II Game played
A F F Table-tennis
B F T Cricket
C T T Football
D T F Tennis
Hence, C always speaks the truth
  1. Who are the two persons who always alternate between the truth and lie?
1. A and D
2. B and C
3. D and B
4. A and C
Option: 3
Explanation: It is known that D plays Tennis, which means that the 2nd statement made by B must be true, whereas the 2nd statement made by D must be false. As A says that he and C both play cricket, A cannot be the person who always speaks the truth, as each person plays exactly one game and exactly one game is played by each person. This means only C can always speak the truth, as there must be at least one person who always speaks the truth.
We take this as the basis and get the arrangement as given below:
  I II Game played
A F F Table-tennis
B F T Cricket
C T T Football
D T F Tennis
Hence, D and B alternate between truth and lie
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