Download SMAM 319 Quiz 9 - RIT

SMAM 319 Quiz 9 Name________________________ A simple random sample of size n=49 is obtained from a population with µ = 80 and σ = 14. A. Find the mean and the standard deviation of the sample mean x . [ Hint: The mean is the population mean and the standard deviation is the population standard deviation divided by n ] µ x = 80
14
σx =
=2
49
B. Find P(78.3 < x < 85.1) by following the steps below. Using your answer to part A either Find the probability with your calculator and give the keystroke or Normalcdf(78.3,85.1,80,2)=.797 (1) Using your answer to Part A find the Z score of 78.3 and 85.1. 78.3 − 80
= −.85
2
85.1 − 80
z2 =
= 2.55
2
z1 =
(2) Look up the cumulative probabilities of these Z scores in the table and complete part B by subtracting these probabilities. For z2 .9946 for z1 .1977 P(78.3 < x < 85.1) =.9946‐.1977=.7969