A local telephone service provider is considering adding a newservice and it wis

A local telephone service provider is considering adding a newservice and it wishes to survey its customers to determine theproportion who would be interested in purchasing the new service. Aresearcher for the company obtains the list of customer phonenumbers ordered according to the prefix. She then uses a randomnumber generator to select a sample of prefixes. She then surveyseach customer with a phone number beginning with one of theselected prefixes. This is an example of: