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.The probability that the sample mean is less than 30 school days is _______.
A) 0.0918
B) 0.4129
C) 0.5871
D) 0.9082

Question

Quizplus · Accepted Answer

The sample mean follows a normal distribution with mean 28 and standard deviation 9/sqrt(36) = 1.5. The z-score for 30 is (30-28)/1.5 = 1.33. The probability of a z-score less than 1.33 is approximately 0.9082.

Over the Entire Six Years That Students Attend an Ohio