iron is always magnetic & glass is always nonmagnetic & aluminum is always nonmagnetic & plastic is always nonmagnetic ->  a mixture of iron, plastic, glass, and aluminum is a mixture of magnetic and nonmagnetic material  a mixture of iron, plastic, glass, and aluminum is a mixture of magnetic and nonmagnetic material & magnet can be used for separating a magnetic material from a mixture of a magnetic and nonmagnetic material -> a magnet can separate iron from plastic, glass, and aluminum