Assignment #5 Confidence Intervals

Z Score Sample Questions:
  1. A manufacturer of salad dressings uses machines to dispense liquid ingredients into bottles that move along a filling line. The machine that dispenses dressings is working properly when 8 ounces are dispensed. The standard deviation of the process is 0.15 ounces. A sample of 50 bottles is selected periodically, and the filling line is stopped if there is evidence that the average amount dispensed is different from 8 ounces. Suppose the average amount dispensed in a particular sample of 50 bottles is 7.983 ounces.

    2. Develop a confidence interval at 95%:

    Answer: Lower limit is 7.948 and upper limit is 8.018 for a 95% confidence interval

 

  • Suppose that the manager of a paint supply store wants to estimate the actual amount of paint contained in 1 - gallon cans purchased from a nationally known manufacturer. It is known from the manufacturer's specifications that the standard deviation of the amount of paint is equal to 0.02 gallon. A random sample of 50 cans is selected, and the average amount of paint per 1-gallon can is 0.995 gallon.
      1. Set up a 99% confidence interval
      2. Set up a 95% confidence interval

    (a). Answer: lower limit .988 and upper limit 1.002

    (b). Answer: lower limit .989 and upper limit 1.001

     

     

     T Score Sample Question:

    1. A new breakfast cereal is test-marketed for 1 month at stores of a large supermarket chain. The results for a sample of 16 store indicate average sales of $1,200 with a sample standard deviation of $180. Set up a 99% confidence interval estimate of the true average sales of this new breakfast cereal.

    Answer: lower limit 1067.40 and upper limit 1332.60

    at 95%: lower limit 1194.54 and upper limit 1205.46

    Click here for calculation model for confidence intervals of the mean