Let an item price rate changes in four consecutive years be as
follows: At the beginning of the first year, the item price was
20%. At the end of the first year, it was increased by 3%. At the
end of the second year, it was increased by 30% relative to its
increased rate during the first year. At the beginning of the
fourth year, it was decreased by 40% relative to its increased rate
during the second year. At the end of the fourth year, it was
increased by 40% relative to its increased rate during the first
year. On average, how much was the item price increased per year in
these four years?