1. The problem statement, all variables and given/known data Suppose A⊂B⊂C. What is A/B, A/C, and A∪B 2. Relevant equations 3. The attempt at a solution This isn't really a homework question, I am just trying to get some exposure to discrete math before I take it in the fall. The set differences A/B and A/C are both empty sets and the 'or' set is B. I understand the last part, but I'm unsure of why A/B and A/C are empty sets. I understand it has something to do with x∈A but x∉B or C as part of the definition of a set difference. I just need someone to explain it to me.