What is the value of an Australian 20 pence coin?

Answer 1

If you are suggesting that you have an Australian 20 cent coin with the same image on both sides, there is almost no chance this could occur with modern minting processes.

Nothing is impossible, but because of the way the dies are fitted together, one side of the coin would have to be incuse, or the image indented into the coin rather than raised. This can be caused by the previously struck coin not being ejected from the die before the new blank was inserted and the incuse image being the result of the new blank being struck against and already struck coin. Coins mistruck in this manner are unlikely to get past the quality control and into circulation.

Most likely, you have a trick or novelty coin sold by magic shops.

Any coin with a "genuine" minting flaw would have some value, above the usual, as a collectible coin.

Genuinely flawed coins are not necessarily known about or documented until somebody turns up with one, since they are an "accident" of the minting process, and have escaped detection during quality control at the mint therefore, a valuation cannot be anticipated.

A reputable coin dealer should be able to identify and confirm the coin as genuine and make a valuation.

Answer 2

Australia has never issued a 20 Pence coin.

All years of issue of the Australian 20 cent coin are potentially still in circulation so, unless they are part of a Proof or Uncirculated mint set or are individual Proof or Uncirculated coins and in absolute mint condition, they are worth 20 cents.