Propositional logic & proofs worksheet with answers

Free printable Propositional logic & proofs worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy
abc(¬b ↔ (b ∧ ¬a)) ∧ (a ↔ c)111110101100011010001000

Exactly one row of the truth table makes (¬b ↔ (b ∧ ¬a)) ∧ (a ↔ c) true. Click that row.

(¬b ↔ (b ∧ ¬a)) ∧ (a ↔ c)
  1. 1a = 1, b = 1, c = 1
  2. 2a = 1, b = 1, c = 0
  3. 3a = 1, b = 0, c = 1
  4. 4a = 1, b = 0, c = 0
  5. 5a = 0, b = 1, c = 1
  6. 6a = 0, b = 1, c = 0
  7. 7a = 0, b = 0, c = 1
  8. 8a = 0, b = 0, c = 0
2.Easy
ab¬((b ∨ a) → (b ↔ ¬a))11100100

Exactly one row of the truth table makes ¬((b ∨ a) → (b ↔ ¬a)) true. Click that row.

¬((b ∨ a) → (b ↔ ¬a))
  1. 1a = 1, b = 1
  2. 2a = 1, b = 0
  3. 3a = 0, b = 1
  4. 4a = 0, b = 0
3.Medium
c ∧ ¬a¬c ↔ ¬ac ↔ ¬a¬c ∨ ¬a

Which formula is logically equivalent to ¬(c ↔ a)? Click it.

¬(c ↔ a)
  1. 1c ∧ ¬a
  2. 2¬c ↔ ¬a
  3. 3c ↔ ¬a
  4. 4¬c ∨ ¬a
4.Medium
pqr¬(q ∧ r)p → ¬(q ∧ r)(q ∧ (p → r)) ∧ (p → ¬(q ∧ r))111?110?101?100?011?010?001?000?

In how many of the 8 rows of its truth table is (q ∧ (p → r)) ∧ (p → ¬(q ∧ r)) true? Call this number N.

(q ∧ (p → r)) ∧ (p → ¬(q ∧ r))
N =
5.Hard
abcb → ac → ab → c111110101100011010001000

The argument with premises b → a; c → a and conclusion b → c is invalid. Click the row of the truth table that is a counterexample.

b → ac → a∴ b → c
  1. 1a = 1, b = 1, c = 1
  2. 2a = 1, b = 1, c = 0
  3. 3a = 1, b = 0, c = 1
  4. 4a = 1, b = 0, c = 0
  5. 5a = 0, b = 1, c = 1
  6. 6a = 0, b = 1, c = 0
  7. 7a = 0, b = 0, c = 1
  8. 8a = 0, b = 0, c = 0
6.Hard
∀x (¬F(x) ∧ ¬G(x))∃x (¬F(x) ∧ ¬G(x))∃x (F(x) → ¬G(x))∀x (F(x) → ¬G(x))

Which statement is equivalent to ¬∃x (F(x) ∧ G(x)), with the negation moved all the way inside? Click it.

¬∃x (F(x) ∧ G(x))
  1. 1∀x (¬F(x) ∧ ¬G(x))
  2. 2∃x (¬F(x) ∧ ¬G(x))
  3. 3∃x (F(x) → ¬G(x))
  4. 4∀x (F(x) → ¬G(x))

Answer key

  1. 1. a = 1, b = 1, c = 1
  2. 2. a = 1, b = 1
  3. 3. c ↔ ¬a
  4. 4. N = 2
  5. 5. a = 1, b = 1, c = 0
  6. 6. ∀x (F(x) → ¬G(x))

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