What is the mathematical formula for ....

My maths is rather rusty.

Could anyone tell me what the mathematical formula is for determining how many unique groups you can make from a finite set of items.

eg. if you have 9 different items, how many unique groups of 3 can you make from that population ?

Permutations {where ORDER is significant}

M! / (M-S)!

Combinations {where order is not significant - like a lottery}

M! / (M-S)! * S!

M = main set of elements
S = subset of elements

Many thanks