Use some thinking to answer the following question. If x, y, and z are positive integers such that x is divisible by y, and y is divisible by z, which of the following is NOT necessarily an integer?
Options:
(A) xy/z
(B) (x + y) /z
(C) xz/y
(D) (x - y) /z
(E) (x + z) /y
As per the question, let x = 12, y = 6, and z = 2. Plugging these into the answer choices, only E does not yield an integer. The reason is that (x + z)/y = x/y + z/y, and while x/y must be an integer, z/y is only an integer if y = z. So the final answer is (E).