A rice mill's husking machine loses 20% of its value in the first year and 10% of its value in each year after that. If it is worth ₹58320 at the end of three years, its purchase price (in ₹) was:

Three years leave $0.80\times 0.90\times 0.90=0.648$ of the price, so the price was 58320/0.648 = ₹90000. (Check: 90000 → 72000 → 64800 → 58320.) Using 10% for all three years, 58320/0.729, gives ₹80000 and forgets the heavier first year; stopping after two years, 58320/0.72, gives ₹81000; and adding the rates to 40% and dividing by 0.60 gives ₹97200 — depreciation compounds downward, it does not add up.