THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:
Suppose that 20% of all invoices are for amounts greater than $800.A random sample of 50 invoices is taken.
-The average score of all students who took a particular statistics class last semester has a mean of 70 and a standard deviation of 3.0.Suppose 36 students who are taking the class this semester are selected at random.Find the probability that the average score of the 36 students exceeds 71.
A)0.0228
B)0.0772
C)0.1228
D)0.1772.

Question

Quizplus · Accepted Answer

The standard error of the mean is 3.0/sqrt(36) = 0.5. The z-score for 71 is (71-70)/0.5 = 2. The probability of a z-score exceeding 2 is 0.0228.