*For example, if the annual expenditure for 2002 was 1000 units and the sequential reductions for the years 2003 to 2005 were respectively 10%, 10% and 20%, then the amount spent on the raw material during 2005 would have been 1000*.9*.9*.8 = 648 units.*

Thus, the amounts spent during 2003, 2004 and 2005 were respectively $L, $M, and $N; the three numbers were positive integers in arithmetic progression.

Determine P, Q and R.