I have a quantity that must be multiplied by a cumulative % factor at each
period over a time series. At each period of this time series I add another
quantity that must then be multiplied by the same series of factors starting
from the beginning. The resulting list of factored quantities in each time
series are totaled. The three components here, the time series, the list of
quantities and the list of factors are quite big so I am looking for a
formula, an array formula or otherwise that will apply these calculations to
these values without having to make a huge array of discrete calculations.
The logic/structure of the data looks like the array below.

Time Period 1 2 3
Factor 90% 93% 95%
Starting Qty1 1000 900 837 795.15
Factor 90% 93%
Starting Qty2 1300 1170 1088.1
Factor 90%
Starting Qty3 1100 990
Total 900 2007 2873.25

I have been trying to find a way to do this with an array formula but I
can't find the way to stagger the new quantities being started up in each
suceeding time period. Anyone got any good ideas about this?
Thanks in advance,
RD Wirr