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Logical Reasoning Fundamentals

Topic in Problem Solving & Analytical Skills

210 total MCQsShowing 30 with explanations10 Easy10 Medium10 Hard

About This Topic

Logical reasoning is the use of formal rules to draw valid conclusions from given premises, ensuring that true premises can never lead to a false conclusion. Practice items evaluate AND, OR, NOT, XOR and implication for given truth values, count truth-table rows (2^n for n variables), and test syllogisms such as deciding what follows from "All cats are animals." Further questions cover contrapositive, converse and inverse, De Morgan's laws, modus ponens and modus tollens, common fallacies like affirming the consequent, the jump from propositional to predicate logic with quantifiers, and how non-monotonic reasoning lets conclusions be withdrawn when new facts arrive.

Below are 30 practice questions from a pool of 210 Logical Reasoning Fundamentals MCQs, one of 16 topics in Problem Solving & Analytical Skills. Each shows the correct answer with an explanation; when you are ready, take a timed quiz to test recall under exam conditions.

Practice Questions

Each question below shows the correct answer with a full explanation. Use these to build conceptual understanding before attempting a timed quiz.

Logical Reasoning FundamentalsEasy

Q1. A=true, B=true. A AND B?

  1. A.True✓ Correct
  2. B.False
  3. C.Null
  4. D.Undefined

Explanation

AND: both true = true.

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Logical Reasoning FundamentalsEasy

Q3. A=true, B=false. A OR B?

  1. A.True✓ Correct
  2. B.Neither
  3. C.Undefined
  4. D.False

Explanation

OR: at least one true = true.

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Logical Reasoning FundamentalsEasy

Q4. General to specific reasoning?

  1. A.Abductive
  2. B.Inductive
  3. C.Analogical
  4. D.Deductive✓ Correct

Explanation

Deductive: general to specific.

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Logical Reasoning FundamentalsEasy

Q5. Specific to general reasoning?

  1. A.Deductive
  2. B.Abductive
  3. C.Inductive✓ Correct
  4. D.Circular

Explanation

Inductive: specific to general.

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Logical Reasoning FundamentalsEasy

Q6. Truth table with 2 variables has how many rows?

  1. A.16
  2. B.4✓ Correct
  3. C.2
  4. D.8

Explanation

4 is the correct answer to this question.

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Logical Reasoning FundamentalsEasy

Q7. What is a logical fallacy?

  1. A.A correct logical argument
  2. B.An error making argument invalid✓ Correct
  3. C.A type of search algorithm
  4. D.A specific data structure

Explanation

Error that renders argument invalid.

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Logical Reasoning FundamentalsEasy

Q8. All cats are animals. Tom is a cat. Therefore?

  1. A.Tom is actually a dog
  2. B.Nothing can be concluded
  3. C.Tom is not an animal
  4. D.Tom is an animal too✓ Correct

Explanation

Classic syllogism: Tom must be an animal.

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Logical Reasoning FundamentalsEasy

Q9. What does XOR return?

  1. A.Always returns true as output
  2. B.True when exactly one is true✓ Correct
  3. C.Always returns false as output
  4. D.True when both inputs are true

Explanation

XOR: exactly one true.

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Logical Reasoning FundamentalsEasy

Q10. What is a premise?

  1. A.A conclusion drawn from evidence
  2. B.A statement assumed true for reasoning✓ Correct
  3. C.A question posed to the audience
  4. D.An error found in the argument

Explanation

Foundation for logical conclusions.

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Logical Reasoning FundamentalsMedium

Q11. Contrapositive of If P then Q?

  1. A.If P then not Q
  2. B.If not Q then not P✓ Correct
  3. C.If Q then P
  4. D.If not P then not Q

Explanation

Contrapositive is logically equivalent.

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Logical Reasoning FundamentalsMedium

Q12. Which is De Morgan's Law?

  1. A.NOT A = A
  2. B.NOT(A AND B) = NOT A OR NOT B✓ Correct
  3. C.A AND B = A OR B
  4. D.A XOR B = A AND B

Explanation

NOT(A AND B) = (NOT A) OR (NOT B).

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Logical Reasoning FundamentalsMedium

Q13. What is modus ponens?

  1. A.P->Q, P false, therefore Q false
  2. B.P->Q, Q false, therefore P false
  3. C.P->Q, Q true, therefore P
  4. D.P->Q, P true, therefore Q✓ Correct

Explanation

If P then Q; P true; Q must be true.

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Logical Reasoning FundamentalsMedium

Q14. What is modus tollens?

  1. A.P->Q, P true, therefore Q
  2. B.P->Q, Q true, therefore P
  3. C.P->Q, Q false, therefore P false✓ Correct
  4. D.P->Q, P false, therefore Q false

Explanation

If P then Q; Q false; P must be false.

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Logical Reasoning FundamentalsMedium

Q15. Truth table with 4 variables?

  1. A.16 rows✓ Correct
  2. B.32 rows
  3. C.8 rows
  4. D.4 rows

Explanation

16 rows is the correct answer to this question.

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Logical Reasoning FundamentalsMedium

Q16. What is a tautology?

  1. A.Always true regardless of values✓ Correct
  2. B.A logical contradiction in reasoning
  3. C.A statement that is always false
  4. D.A statement that is sometimes true

Explanation

True under every interpretation.

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Logical Reasoning FundamentalsMedium

Q17. What is a contradiction?

  1. A.Always false regardless of values✓ Correct
  2. B.A tautology under all conditions
  3. C.A valid argument with true premises
  4. D.A statement that is always true

Explanation

False under every interpretation.

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Logical Reasoning FundamentalsMedium

Q18. What does P <-> Q mean?

  1. A.P implies Q in one direction only
  2. B.P is true if and only if Q is true✓ Correct
  3. C.Q implies P in one direction only
  4. D.Both P and Q are always true together

Explanation

Biconditional: same truth value.

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Logical Reasoning FundamentalsMedium

Q19. What is proof by contradiction?

  1. A.A type of mathematical induction
  2. B.Proving the statement is false
  3. C.A direct proof from axioms
  4. D.Assume opposite, show contradiction✓ Correct

Explanation

Assumes negation, derives contradiction.

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Logical Reasoning FundamentalsMedium

Q20. Affirming the consequent fallacy?

  1. A.Rain->wet. No rain. Not wet.
  2. B.Rain->wet. Dry. No rain.
  3. C.Rain->wet. Wet. Therefore rained.✓ Correct
  4. D.Rain->wet. Rained. Wet.

Explanation

Ground could be wet for other reasons.

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Logical Reasoning FundamentalsHard

Q21. Universal quantifier means?

  1. A.For exactly one element only
  2. B.For all elements in the domain✓ Correct
  3. C.For no elements in the domain
  4. D.There exists at least one element

Explanation

For all elements in the domain.

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Logical Reasoning FundamentalsHard

Q22. Negation of forall x P(x)?

  1. A.exists x NOT P(x)✓ Correct
  2. B.forall x NOT P(x)
  3. C.NOT exists x P(x)
  4. D.forall x P(x) still

Explanation

Not all = there exists one that is not.

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Logical Reasoning FundamentalsHard

Q23. What is mathematical induction?

  1. A.Proving base case plus if n then n+1✓ Correct
  2. B.Testing all possible cases manually
  3. C.Guessing the answer to the problem
  4. D.Only proving the base case alone

Explanation

Base case plus inductive step.

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Logical Reasoning FundamentalsHard

Q24. What is a clause in resolution?

  1. A.A disjunction of logical literals✓ Correct
  2. B.A conjunction of several functions
  3. C.A complete executable program
  4. D.A variable assignment statement

Explanation

Clause = disjunction (OR) of literals.

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Logical Reasoning FundamentalsHard

Q25. Logical completeness means?

  1. A.The system runs very fast
  2. B.The system has no bugs at all
  3. C.Every valid formula is provable✓ Correct
  4. D.It uses all logical operators

Explanation

Every valid formula is derivable.

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Logical Reasoning FundamentalsHard

Q26. Godel's first incompleteness theorem?

  1. A.All formal systems are complete
  2. B.All true statements are provable
  3. C.Consistent systems have unprovable truths✓ Correct
  4. D.Logic is unnecessary for proofs

Explanation

Sufficiently powerful systems have unprovable truths.

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Logical Reasoning FundamentalsHard

Q27. What is satisfiability (SAT)?

  1. A.Whether an assignment makes it true✓ Correct
  2. B.A formula that is always true
  3. C.A formula with no variable bindings
  4. D.A formula that is always false

Explanation

First proven NP-complete problem.

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Logical Reasoning FundamentalsHard

Q28. What is soundness?

  1. A.It uses auditory signal processing
  2. B.The system proves everything possible
  3. C.The system has zero error states
  4. D.Every provable statement is valid✓ Correct

Explanation

Only true statements can be proven.

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Logical Reasoning FundamentalsHard

Q29. SAT worst case?

  1. A.O(n^2) quadratic time
  2. B.O(n) linear time
  3. C.Exponential (NP-complete)✓ Correct
  4. D.O(n log n) linearithmic

Explanation

NP-complete: exponential worst case.

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Logical Reasoning FundamentalsHard

Q30. What is semantic entailment?

  1. A.A programming concept for objects
  2. B.A specific data type for storage
  3. C.A syntax rule in formal languages
  4. D.Premises true implies conclusion true✓ Correct

Explanation

Truth of premises guarantees truth of conclusion.

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