Question

This is a stats question, but I'm hoping someone will be able to help. how many different ways to arrange the letters in Mississippi are there assuming letters are not distinct and no two I's can be next to each other? The answer is 8 choose 4x (7!/4!2!1!). I understand 7!/4!2!1! is the ways to rearrange the letters that are not I, and that 8 choose 4 is the ways to arrange I so that no two are next to each other. I don't understand how they come up with 8 choose 4.