use a running total with an evaluation formula (or use shared variable formulas that do the same thing)
right click on Running Total ans selcet new
Name=whatever
Field to summarize=number of member field
type = sum
evaluate=use a formula
right(table.name,3)<>'INC'
reset=on change of group (for group totals)
place in group footer
--RTs do not work in headers
Repeat a seonc RT for the grand total but make the reset=never