Solutions to Selected Problems
Z for 90th percentile=1.282
What is the probability that the mean HDL cholesterol among these 40 patients is less than 50?
From the standard normal distribution table P(Z<-1.48)=0.0694.
Therefore, the probability that the mean HDL among these 40 patients will be less that 50 is 6.94%.
It is extremely unlikely (probability very close to 0) to observe a Z score exceeding 6.67. There is virtually no chance that in a sample of 50 women their mean alpha fetoprotein exceeds 75.