I am guessing this have more to do with the Desc type than the numbers.
If you have consitent useage of the descriptions types you can build two Running Totals and then use those for a formula.
name=RT1
type=sum
field to summarize=pmonth
evaluate=use a formula
ttable.desc in ['PCash','HC Fund']
reset = never (assuming you do not have group level data totals)
name=RT2
type=sum
field to summarize=pmonth
evaluate=use a formula
ttable.desc in ['Rem','Deposit','Float']
reset = never (assuming you do not have group level data totals)
your final fomrual would be soomething like
#RT1 + (if #RT2 is >0 then #RT2 else 0)