On Saturdays, Cars Arrive at David Zebda's Scrub and Shine

Multiple Choice

On Saturdays, cars arrive at David Zebda's Scrub and Shine Car Wash at the rate of 80 cars per hour during the ten-hour shift.David wants a sample of 40 Saturday customers to answer the long version of his quality service questionnaire.He randomly selects 9 as a starting point and instructs the crew to select the 9th customer and every 20^th customer thereafter (9, 29, 49, etc.) .His sample is a __________.

A) convenience sample
B) simple random sample
C) unsystematic sample
D) stratified sample
E) systematic sample