get the sum of a sequence of numbers

I think this should be easy to do but techniques I am using arent working.

I have template that returns the word count of topics that contain language attributes and assigns it to a sequence. T

Problem is that when I want total the numbers stored in the sequence using <xsl:variable name="mbt" select="sum(number($mb))"/> what I get are the numbers concatenated together when what I want is the total sum of the values of numbers of which the list consists.  Suggestions on the correct way to do this in XSL2.0? thanks.
 
--------------------Karen McAdams