You find that the unknown powder contains the illegal drug cocaine. If someone where to ask you to determine the purity of the substance, what would they mean? Why is purity important in crime investigations?

The substance is not composed entirely of cocaine, it is mixed with other materials. The purity refers to what percentage of the powder is cocaine, and what percentage is other materials.

Purity can be important in crime investigations to find out the samples value, and to pair it with previously found samples of equal purity to deduce that they came from the same source.