NPTEL Artificial Intelligence: Knowledge Representation And Reasoning Week 2 Assignment Answers 2025
1. A sentence in logic is a statement that in principle has a truth value. Which of the following are sentences in logic?
- Did Joe pardon his son?
- Joe said he will not pardon his son.
- Joe did not pardon his son.
- Please sign a law banning voter ID.
- Governor signed a law banning voter ID.
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2. Select the reasoning method(s) that lead to logically sound arguments
- Abduction
- Deduction
- Both of the above
- None of the above
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3. Select the formulas that are tautologies.
- P ⊃ (¬P ⊃ P)
- (P ⊃ P) ⊃ ¬P
- ¬P ⊃ (P ⊃ P)
- (P ⊃ Q) ∨ (Q ⊃ R)
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4. Given three formulas P, Q and R, a rule of inference such as {P, Q} ⊢ R is said to be valid if and only if ________________ .
- ((P ∧ Q) ⊃ R) is satisfiable
- ((P ∧ Q) ⊃ R) is a tautology
- (¬P ∨ ¬Q ∨ R) is satisfiable
- (¬P ∨ ¬Q ∨ R) is a tautology
- (P ∧ Q ∧ ¬R) is satisfiable
- (P ∧ Q ∧ ¬R) is a tautology
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5. Select the valid rules of substitution.
- [¬(P ⊃ Q)] ≡ [¬P ⊃ ¬Q]
- [P ⊃ Q] ≡ [¬Q ⊃ ¬P]
- [¬P ⊃ ¬Q] ≡ [P ∨ ¬Q]
- [P ⊃ R] ⊃ [(P ∧ Q) ⊃ R]
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6. Select the valid rules of inference.
- {P ⊃ Q, P} ⊢ Q
- {P ⊃ Q, ¬P} ⊢ ¬Q
- {P ∧ Q} ⊢ (P ∨ Q)
- {P ⊃ R} ⊢ ((P ∧ Q) ⊃ R)
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7. Which of the following sets of connectives are complete in propositional logic?
- {NAND}
- {⊃}
- {∧,¬}
- {∨,¬}
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8. A knowledge base (KB) written in a logic language is ______________ .
- a set of sentences where all the sentences in that set are true
- a set of sentences where some sentences may be false because we need the ability to represent what is false
- none of these
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9. In propositional logic, what does it mean to say that a KB entails P (symbolically, KB ⊨ P)?
- When all the sentences in KB are true then P is necessarily true.
- One can derive P from the sentences in the KB.
- All of the above
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10. What does (KB ⊢ P) mean?
- KB entails P.
- KB derives P.
- All of the above.
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11. A proof or derivation in logic is ____________ .
- a syntactic process that uses inference rules to generate new formulas from existing formulas
- a syntactic process that does not bother with the truth values of the sentences that are begin read and/or derived
- an evaluation function that uses the truth values of existing formulas to derive truth values for new formulas
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12. Consider four proof procedures (derivation algorithms) A, B, C, D. The quality of the sentences derived by each procedure is depicted below.

Select the procedure(s) that are sound.
- Procedure A
- Procedure B
- Procedure C
- Procedure D
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13. Select the procedure(s) that are complete.
- Procedure A
- Procedure B
- Procedure C
- Procedure D
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14. Observation: dry vegetation causes wildfires in the Santa Monica Mountains.
D: There is dry vegetation.
W: There is a wildfire.
Which of the following is the correct logic-based representation of the connection between the presence of dry vegetation and the presence of wildfire?
(Hint: choose the formula that produces acceptable output under all scenarios: presence/absence of dry vegetation and presence/absence of wildfire.)
- W ∧ D
- W ∨ D
- W ⊃ D
- D ⊃ W
- (W ⊃ D) ∧ (D ⊃ W)
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15. Is the following argument valid?
If there is a wildfire then houses will burn to cinders.
The houses were burnt to cinders.
Therefore, there was a wildfire.
- Yes
- No
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16. Is the following argument valid?
If there is a wildfire then houses will burn to cinders.
The houses did not burn, they remained intact.
Therefore, there was no wildfire.
- Yes
- No
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17. Is the following argument valid?
He must have fire insurance or he must have huge savings.
He has zero savings.
Therefore, he has fire insurance.
- Yes
- No
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18. Is the following argument valid?
He must have fire insurance or he must have huge savings.
He has massive savings.
Therefore, he has no fire insurance.
- Yes
- No
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19. Frege’s Propositional Calculus uses only ________________ and ___________ connectives
- AND (∧)
- EQUIVALENCE (≡)
- IMPLIES (⊃)
- NAND (↑)
- NOR (↓)
- NOT (¬)
- OR (∨)
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20. Modus Ponens _______________ .
- is a proof procedure
- is a valid inference rule
- is used to compute the truth values of compound sentences
- all of the above
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