To gather information on customer satisfaction, a researcher randomly selects four store locations and interviews all the customers at those selected stores. This sampling technique is called:

This sampling technique is called cluster

Step-by-step explanation:

Samples may be classified as:

Convenient: Sample drawn from a conveniently available pool.

Random: Basically, put all the options into a hat and drawn some of them.

Systematic: Every kth element is taken. For example, you want to survey something on the street, you interview every 5th person, for example.

Cluster: Divides population into groups, called clusters, and each element in the cluster is surveyed.

Stratified: Also divides the population into groups. However, then only some elements of the group are surveyed.

In this question:

The population is divided into groups(by stores), and all elements of the groups(all customers at the stores are sampled), which is the characteristic of a cluster sampling.

9 x 8 divided by (5-3)=36