You do not give any detail to identify the notes.
Presumably they are in mint or uncirculated condition.
A group of sequentially numbered notes would have some value above that of the same number of non-sequentially numbered notes.
The Reserve Bank of Australia advises that there are approximately 132,600,000 Australian Twenty Dollar notes in circulation as at 30th of June, 2009.
cheak on Museum of Australian Currency Notes
The first Australian Twenty Dollar notes, along with the One, Two and Ten Dollar notes, were issued on the 14th of February, 1966 for the introduction of Australia's new decimal currency.
Australia does not have a "percent" note. Current circulating Australian banknotes are the Five, Ten, Twenty, Fifty and One Hundred Dollar notes.
It would depend on the condition of the notes, but generally, the 1975 notes are worth more.
The first Australian One Dollar note along with the Two, Ten and Twenty Dollar notes, were issued on the 14th of February, 1966, at Australia's conversion to decimal currency. The first Australian One Dollar coin was issued in 1984.
The first Australian One Dollar notes were issued in 1966 at the introduction to decimal currency. The last Australian One Dollar notes were issued in 1982. They were replaced with a One Dollar coin in 1984 and progressively withdrawn from circulation.
The last Australian One Dollar notes were printed in 1982. The Australian One Dollar coin was first issued in 1984. The One Dollar notes were progressively withdrawn from circulation from 1984.
The last Australian Two Dollar notes were printed in 1985. The Australian Two Dollar coin was first issued in 1988. The Two Dollar notes were progressively withdrawn from circulation from 1988.
There were no 1968 Australian Five Dollar notes printed.
There were no Australian Fifty Dollar notes printed in 1984.
Plastic (polymer)