9. Use your data to find a range of likely values for average sales for all representative in the entire company using StatCrunch. Ven_fy' with your own calculations and show your work. FINDING A CONFIDENCE INTERVAL FOR THE POPULATION MEAN USING STATCRUNCH. In this case you know the population standard deviation a. --Mystatlab.com I StatCrunch / Open StatCrunch. --Go to "STATSIZ STATS/ONE SAMPLE! WITH SUMMARY. --In the window, type in the mean, standard deviation, and sample size. (Note it says sample standard deviation but it should say population standard deviation.) --Hit COMPUTE! You will get the Upper Limit and the Lower Limit of your condence interval. Include a statement with it. 10. The average sales for the entire company last year was reported to be $100 million. According to your results from the previous problem, do you think the average sales have changed this year? Why or why not? If so, how has it changed? (Hint: Think about what your range of likely values is for average sales.) 11. Scores on an MBA placement exam are reported to have a normal distribution with standard deviation 18. The exam officials stated that the average score for all students was 70. You take a random sample of 50 students and find their average score is 67. Use your data to estimate the mean score for all students taking the MBA placement exam using StatCrunch. Verify your answer using calculations and show your work. 12. Students at the union want to estimate the average number of ounces of coffee in a cup. They take a random sample of 40 cups and find the mean is 5.2 ounces. Assume amount dispensed has a normal distribution and that the standard deviation is set at 0.24 ounces per cup. Find your best estimate for the average amount of coffee being dispensed by this machine. Use StatCrunch. Veri our answer usin calculations and show our work. FOR THE NEXT 4 PROBLEMS (#13- 16): You want to estimate the average household income for Ohio. You want the margin of error to be no more than $1,000. Prior data shows the standard deviation of household income is $30,000. 13. How many households should we sample to achieve the desired margin of error? 14. Suppose you want to cut the margin of error down to $500 next time. What should your sample size be? 15. Suppose you want to cut the margin down to 1/3 of what it started at (1/3 of 1000). What does your sample sizes have to be? (Be careful!) 16. Why do we always round up when finding the appropriate sample size to achieve a certain margin of error, even when the value after the decimal point is less than .5? (For example, if we solve for n and get 422.2 households, why do we round this up to 423 households when reporting the required It?)
