This article describes the formula syntax and usage of the COMBIN function in Microsoft Excel.
Description
Returns the number of combinations for a given number of items. Use COMBIN to determine the total possible number of groups for a given number of items.
Syntax
COMBIN(number, number_chosen)
The COMBIN function syntax has the following arguments:

Number Required. The number of items.

Number_chosen Required. The number of items in each combination.
Remarks

Numeric arguments are truncated to integers.

If either argument is nonnumeric, COMBIN returns the #VALUE! error value.

If number < 0, number_chosen < 0, or number < number_chosen, COMBIN returns the #NUM! error value.

A combination is any set or subset of items, regardless of their internal order. Combinations are distinct from permutations, for which the internal order is significant.

The number of combinations is as follows, where number = n and number_chosen = k:
where:
Example
Copy the example data in the following table, and paste it in cell A1 of a new Excel worksheet. For formulas to show results, select them, press F2, and then press Enter. If you need to, you can adjust the column widths to see all the data.
Formula 
Description 
Result 
=COMBIN(8,2) 
Possible twoperson teams that can be formed from 8 candidates. 
28 