Asample of 100 janitors in a certain school district found that the average time each janitor had worked for the school district was 8 years. suppose we know that the standard deviation of the population is s=5 years. construct a 95% confidence interval for the mean time of the population of janitors have spent with the school district.
a) 8±1.98
b) 8±0.82
c) 8±0.71
d) 8±1.53
e) 8±0.98