Is there sum and average functions for the spreadsheet widget?

Yes, it is possible to make sum and aaverage functions for the spreadsheet widget, you only have to include the sum/average formula accordingly.

Take a look at the following exmple:

As for instance, you have a spreadsheet of 10 rows and 10 columns, the formulas to get sum of rows from cells C thoroug H will be shown on cell I, the average will be showed on cell J

To get results on Cells I and J, I used the following formulas.

i2 = c2 + d2 + e2 + f2 +g2 + h2

j2 = i2/6

I hope this information helps.