Final answer:
Without additional data regarding the number of customers served by each server, we cannot determine which set of servers served fewer than 20 customers at lunch. Roster form is used to list elements of a set, and accurate data is required for statistical analysis.
Step-by-step explanation:
To answer the question, we need to find the set of servers who served fewer than 20 customers at lunch and write the set in roster form. The question does not provide enough specific data to determine which set of servers meets this criterion. Therefore, we cannot select from options (s1, s3, s5, s7), (s2, s4, s6, s8), (s1, s2, s3, s4), or (s5, s6, s7, s8) without additional information. Gathering accurate data (potentially a roster with the number of customers served by each server) is essential for determining the correct set.
Without the specific data, the question related to the topic of using roster form to represent sets in mathematics is unanswerable. Roster form is a way of representing a set by listing its elements between braces. Complete and accurate data would be required to choose a simple random sample or to make any other statistical judgements like those mentioned regarding an exponential distribution for customer arrivals.