What is the difference between a preserved and petrified fossil?

A preserved fossil has been stored for many years even millions. Such as a Wooly Mammoth. However, a petrified fossil only becomes a fossil after certain material has been replaced or taken out from the organism. 

Best A petrified wood is one that has been replaced with minerals. A fossil is any evidence of life that has been preserved in rock. Petrified means fossilized.Minerals replaced once living material, such as wood, creating a rock replica
Fossils: remains or traces of plant or animal life found in rocks

Petrified: process in which once living things turn to stone

Amath expression is a collection of one or more terms, which are separated by the signs ( + , - , x , / ).example :   8+b8+b  or  a−3a−3in algebra, an equation is a mathematical statement with two expressions where, each expression is separated by an equal (=) sign. variables can be present on both the sides of the equality (=) sign and we use letters to denote such variables.example 1:   x=4+2x=4+2  , [here, we can observe that the variable is present only on one side of the equation].example 2:   2x+3=x+42x+3=x+4  , [here, we can observe that the variables are present on both side of the equation].

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