If x ∈ , what is the largest possible result of x mod 18?

Consider the function f : {a, b, c} → {1, 2, 3} defined by f(a) = 1, f(b) = 1, f(c) = 2. What is f^-1({1, 3})?

What is the intersection of A and B (A∩B)?

A = {a, b, c}

B = {c, d}

What is the contrapositive of the following statement...

If X then Y

What is the union of A and B (A∪B)?

A = {a, b, c}

B = {c, d}

Which of the following is NOT a valid set?

X = {1, 3, 2}

Y = {1, {2, 3}}

Z = {}

Use exhaustive checking to prove or disprove the following statement...

There is a prime number between 45 and 54.

Is this statement true based on your analysis?

True or False: 

The symmetric difference between two sets (A and B) is the set that includes every element that is either in A or B but NOT elements that are in both A and B. This is similar to the Boolean XOR operator ⊕. 

True or False?

Two statements are said to be equivalent if they have the same truth value for any assignment of truth values to the variables that occur in the statements

Which of the following statements is the conjunction of X and Y?