Over the entire six years that students attend an ohio elementary school, they are absent, on average, 28 days due to influenza. assume that the standard deviation over this time period is σ = 9 days. upon graduation from elementary school, a random sample of 36 students is taken and asked how many days of school they missed due to influenza. what is the standard deviation for the sampling distribution of the average number of school days missed due to influenza?