If an index is based on 3 columns will a query using two of the columns utilize the index?

Example:
assume a table of 10 columns, three of which are fname, lname, and dob.
If an index is created on (fname, lname, dob), will a query that
utilizes two of the columns ( select 'data' from table where fname = 'X'
and lname = 'Y') utilize the index?

thanks,
reid