Intersection (set theory)

When we talk about an "intersection" in set theory, we are basically talking about finding the stuff that is the same in two groups of things. Imagine you have two boxes with different items in them - let's say one box has a pencil, an eraser, and a ruler, and the other box has a pencil, a pen, and a stapler. Now, if you ask "What is in both boxes?" you would be asking for the intersection of the two sets - or in other words, the things that are in both sets.

So, the intersection between these two boxes would be just the pencil - because that's the only item that both boxes contain. In set theory, we write that like this:

Intersection of Set A and Set B = {Pencil}

We can also use a symbol to represent this - it looks like an upside down 'U' and means "intersection". So, if we wanted to write the same thing using the intersection symbol, we would write:

A ∩ B = {Pencil}

Basically, the intersection is just a way of finding the things that two sets have in common. It's like when you and a friend both have the same favorite color or both like the same game - that's your intersection! In set theory, we're just doing that same thing with two groups of things, and using some symbols to make it easier to write down.