Question

If A ⊂ B, then A ∩ B = A ∪ B. Sometimes, Always, or Never?

Answer 1

Let's make up an example - suppose B = {1, 2, 3, 4}, and A is a subset of B, so
A = {1, 2}

Answer 2

A ∩ B = all elements that are in both, so A ∩ B = {1, 2}

Answer 3

A U B = union, so just everything that's in either set = {1, 2, 3, 4}
See in this case A ∩ B does not equal A ∪ B.

Answer 4

Now make up an example where A ∩ B = A ∪ B

Answer 5

Oh and where A is a subset of B (hint every set is a subset of itself)

Answer 6

Come on, at least try to come up with something.