sum « XSLT stylesheet « XML Tutorial

5.13.1.sum()- Takes a node-set as its argument and returns the sum of the value of each individual node after converting the values to a numeric type if possible.
5.13.2.round the result of sum()
5.13.3.Sum value
5.13.4.sum() sums all numbers in selected nodes.
5.13.5.sum only odd ones