Apple iWork '09 - Manual (Page 172)

COMBIN
The COMBIN function returns the number of different ways you can combine a
number of items into groups of a specific size, ignoring the order within the groups.
COMBIN(total-items, group-size)
 total-items: The total number of items. total-items is a number value and must be
greater than or equal to 0. If total-items has a decimal (fractional) part, it is ignored.
 group-size: The number of items combined in each group. group-size is a number
value and must be greater than or equal to 0. If group-size has a decimal (fractional)
part, it is ignored.
Usage Notes
Combinations are not the same as permutations. The order of the items in a group is Â
ignored for combinations but not for permutations. For example, (1, 2, 3) and (3, 2, 1)
are the same combination but two unique permutations. If you want the number of
permutations rather than the number of combinations, use the PERMUT function.
Examples
=COMBIN(3, 2) returns 3, the number of unique groups you can create if you start with 3 items and
group them 2 at a time.
=COMBIN(3.2, 2.3) returns 3. Fractional parts are dropped.
=COMBIN(5, 2) and =COMBIN(5, 3) both return 10.
Related Topics
For related functions and additional information, see:
“PERMUT” on page 281
“Listing of Numeric Functions” on page 167
“Value Types” on page 36
“The Elements of Formulas” on page 15
“Using the Keyboard and Mouse to Create and Edit Formulas” on page 26
“Pasting from Examples in Help” on page 41
172 Chapter 8 Numeric Functions