The administration of a hospital wanted to estimate the average length of stay of in-patients during the last year. Medical records of 40 randomly selected patients whostayed in the hospital in the last year showed that 15 of them stayed for 2 days, 15for 3 days, and 10 for 4days. What is the population in this study?The 40 randomly selected patientsThe 15 patients who stayed for 2 daysAll in-patients during the last year