Math Help - Dividing objects in to groups.

1. Dividing objects in to groups.

Hi,

I hope I've put this in the right area. It's been a long time since I've been in school

What I'd to know is the formula for how to solve a problem like:

There are 30 unique hats/cars/whatever and you have to select 4. How many unique combinations of 4 hats/cars/whatever is there?

I don't need an answer for this specific question, just a poke in the right direction.

Thank you, this seems like a wonderful resource.

2. Without repitition, it would be:

$30C4 = \dbinom{30}{4} = \dfrac{30!}{4! \times (30-4)!}$