I would like to sum the numbers in a column that coincide with the rows where
the numbers in two other columns meet a certain condition.

For example, I need to find all rows where column A and column B have a
value of one; then the corresponding values for those rows in column C need
to be summed. I thought this may be a sumif formula, however I don't know if
more than one function can be nested in a sumif formula.

Any help with this would be greatly appreciated.
--
Valerie