Manufacturers were subdivided into groups by volume of sales. Those with more than $100 million in sales were classified as Class A large; those from $50 to $100 million as Class A medium size; those between $25 and $50 million small, and so on. Samples were then selected from each of these groups. What is this type of sampling called?

Explanation: This is stratified random sampling. It is a method of selecting a random item from each section of the population. The randomness comes from the random selection from a particular section. Stratified refers to the division of the sections.