The Intelligence Quotient (IQ) test scores are normally distributed with a mean of 100 and a standard deviation of 15. Given a class with 9 students, what is the probability that the class' average IQ score is between 85 and 115?
A) 0.4987
B) 3.00
C) 0.0026
D) 0.9974

Question

Quizplus · Accepted Answer

The sampling distribution of the sample mean for 9 students will have the same mean (100) but a standard deviation of 15/sqrt(9) = 5. The probability that the sample mean is between 85 and 115 can be found using the standard normal distribution, resulting in approximately 0.9974.

The Intelligence Quotient (IQ) Test Scores Are Normally Distributed with a Mean