ComponentOne DataGrid for Silverlight includes the C1.Silverlight.DataGrid.Summaries.dll assembly which can enhance the grid by adding a summary row.
The Summaries assembly contains the following features:
•SummaryRow. a row that shows the aggregate functions corresponding to each column (See C1DataGrid_Demo2010/Grouping/GrandTotal.xaml)
•GroupRowWithSummaries the same as the previous one but the summaries are shown in the group row rather than a regular row. (See C1DataGrid_Demo2010/Grouping/Grouping.xaml)