WGU D420 Discrete Math 1 Exam (2025/2026)
Updated: EXAM QUESTIONS WITH ACCURATE
ANSWERS | GET IT RIGHT!!
Exclusive or. ⊕ - (ANSWER)One or the other, but not both.
We can go to the park or the movies.
inclusive or is a: - (ANSWER)disjunction
Order of operations in absence of parentheses. - (ANSWER)1. ¬ (not)
2. ∧ (and)
3. ∨ (or)
the rule is that negation is applied first, then conjunction, then disjunction:
truth table with three variables - (ANSWER)see pic
2^3 rows
proposition - (ANSWER)p → q
Ex: If it is raining today, the game will be cancelled.
Converse: - (ANSWER)q → p
If the game is cancelled, it is raining today.
,Contrapositive - (ANSWER)¬q → ¬p
If the game is not cancelled, then it is not raining today.
Inverse: - (ANSWER)¬p → ¬q
If it is not raining today, the game will not be cancelled.
biconditional - (ANSWER)p ↔ q
true when P and Q have the same truth value.
see truth table pic.
free variable - (ANSWER)ex.
P(x)
the variable is free to take any value in the domain
bound variable - (ANSWER)∀x P(x)
bound to a quantifier.
In the statement (∀x P(x)) ∧ Q(x), - (ANSWER)the variable x in P(x) is bound
,the variable x in Q(x) is free.
this statement is not a proposition cause of the free variable.
summary of De Morgan's laws for quantified statements. - (ANSWER)¬∀x P(x) ≡
∃x ¬P(x)
¬∃x P(x) ≡ ∀x ¬P(x)
using a truth table to establish the validity of an argument - (ANSWER)see pic.
In order to use a truth table to establish the validity of an argument, a truth table
is constructed for all the hypotheses and the conclusion.
A valid argument is a guarantee that the conclusion is true whenever all of the
hypotheses are true.
If when the hypotheses are true, the conclusion is not, then it is invalid.
the argument works if every time the hypotheses (anything above the line) are
true, the conclusion is also true.
, hypotheses dont always all need to be true, see example. but every time all the
hypotheses are true, the conclusion needs to be true as well.
rules of inference. - (ANSWER)see pic.
theorem - (ANSWER)any statement that you can prove
proof - (ANSWER)A proof consists of a series of steps, each of which follows
logically from assumptions, or from previously proven statements, whose final
step should result in the statement of the theorem being proven.
the proof of a theorem may make use of axioms: - (ANSWER)which are
statements assumed to be true.
proofs by exhaustion - (ANSWER)trying everything in the given universe.
proofs by counter example - (ANSWER)show that one fails.
A counterexample is an assignment of values to variables that shows that a
universal statement is false.
A counterexample for a conditional statement must satisfy all the hypotheses and
contradict the conclusion.
direct proofs - (ANSWER)used for conditional statements
Updated: EXAM QUESTIONS WITH ACCURATE
ANSWERS | GET IT RIGHT!!
Exclusive or. ⊕ - (ANSWER)One or the other, but not both.
We can go to the park or the movies.
inclusive or is a: - (ANSWER)disjunction
Order of operations in absence of parentheses. - (ANSWER)1. ¬ (not)
2. ∧ (and)
3. ∨ (or)
the rule is that negation is applied first, then conjunction, then disjunction:
truth table with three variables - (ANSWER)see pic
2^3 rows
proposition - (ANSWER)p → q
Ex: If it is raining today, the game will be cancelled.
Converse: - (ANSWER)q → p
If the game is cancelled, it is raining today.
,Contrapositive - (ANSWER)¬q → ¬p
If the game is not cancelled, then it is not raining today.
Inverse: - (ANSWER)¬p → ¬q
If it is not raining today, the game will not be cancelled.
biconditional - (ANSWER)p ↔ q
true when P and Q have the same truth value.
see truth table pic.
free variable - (ANSWER)ex.
P(x)
the variable is free to take any value in the domain
bound variable - (ANSWER)∀x P(x)
bound to a quantifier.
In the statement (∀x P(x)) ∧ Q(x), - (ANSWER)the variable x in P(x) is bound
,the variable x in Q(x) is free.
this statement is not a proposition cause of the free variable.
summary of De Morgan's laws for quantified statements. - (ANSWER)¬∀x P(x) ≡
∃x ¬P(x)
¬∃x P(x) ≡ ∀x ¬P(x)
using a truth table to establish the validity of an argument - (ANSWER)see pic.
In order to use a truth table to establish the validity of an argument, a truth table
is constructed for all the hypotheses and the conclusion.
A valid argument is a guarantee that the conclusion is true whenever all of the
hypotheses are true.
If when the hypotheses are true, the conclusion is not, then it is invalid.
the argument works if every time the hypotheses (anything above the line) are
true, the conclusion is also true.
, hypotheses dont always all need to be true, see example. but every time all the
hypotheses are true, the conclusion needs to be true as well.
rules of inference. - (ANSWER)see pic.
theorem - (ANSWER)any statement that you can prove
proof - (ANSWER)A proof consists of a series of steps, each of which follows
logically from assumptions, or from previously proven statements, whose final
step should result in the statement of the theorem being proven.
the proof of a theorem may make use of axioms: - (ANSWER)which are
statements assumed to be true.
proofs by exhaustion - (ANSWER)trying everything in the given universe.
proofs by counter example - (ANSWER)show that one fails.
A counterexample is an assignment of values to variables that shows that a
universal statement is false.
A counterexample for a conditional statement must satisfy all the hypotheses and
contradict the conclusion.
direct proofs - (ANSWER)used for conditional statements
