To make them harder to counterfeit.
It also makes it more obvious if the edge has been shaved for the gold or silver.
The idea was suggested by Master of the Mint Sir Isaac Newton.
The more common name for this practice is "reeding".
Numismatics is the study of coins.
A sphere fits the given description
No, not every possible minimal spanning tree of a given graph has an identical number of edges.
If you mean 6 faces and 12 edges then a cube would fit the given description which also has 8 vertices.
Tokens
ALL us minted coins by stated value for a given year
There is not a polyhedron with the given number of faces, edges and vertices.
A cube or a cuboid would fit the given description of 12 edges and 6 faces.
strange change
Space
There are no 20cent coins. And you can't solve that question with the information given. You need the dimensions of the coins
A cylinder would fit the given description.