Question

Is the set of multiples of 4 closed under addition? Explain why or provide a counterexample if not.

A.
Yes, because the sum of any two multiples of 4 is also a multiple of 4.

B.
Yes, because the sum of any two multiples of 4 is also a multiple of 8.

C.
No, and a counterexample is –4 + (–8) = –12.

D.
No, and a counterexample is 26 + 16 = 42.