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BA501
: The Class
: Stats :
Intervals
: Home Work
Sampling Distributions:
Home Work
To complete this assignment successfully, you should:
§ Sampling Distributions and Confidence Intervals §
Assignments
Send to your instructor a single
Excel file (including written answers) as e-mail an attachment through WebMail. addressed
to BA501@mail.cba.nau.edu and put "BA501
(last name) Assignment name and number" somewhere in the
e-mail "subject." If you have any questions on this home work, please
e-mail me with questions.
Put the different exercise outputs on separate sheets in the Excel file.
Here is the
Excel
worksheet for this assignment. Use "save as"
to save it to your computer or to a floppy.
Exercise 1
A computer hardware firm has a group of employees who load software on to PCs. It is assumed that the time it takes an employee to load a PC is normally distributed with a mean time of 35 minutes and a standard deviation of 5 minutes. Use Excel to answer these questions.
(click me)
(a) What is the probability that an employee will spend less than 30 minutes to load software on a PC?
(b) In a randomly selected sample of 9 employees, what is the probability that the average time it takes them to load software on to PCs is less than 30 minutes?
Exercise 2
A paint company engineer believes that the thickness of paint sprayed on new cars follows a uniform distribution. A sample of 64 new cars paint jobs yielded a sample mean of 0.36 inches with a standard deviation of 0.09 inches. Find a 90% confidence interval for the mean thickness of paint sprayed on new cars. Use Excel to find the confidence interval. Give the three intrepretations of this confidence interval.
(click me)
Exercise 3
A random variable is found to range from a high of 75 to a low of 50 from past data. The distribution of the random variable can be approximated by a normal distribution. To estimate the mean of the variable to within 4.2, what sample size would be necessary in selecting a random sample to achieve a 98% confidence level?
(click me)
Exercise 4
The heights of females students in Arizona is know to follow a normal distribution. A sample of 14 females yields the following heights in inches. Construct a 90% confidence interval for the mean heights of females in Arizona. Use Excel to do the calculations. Give the three intrepretations of this confidence interval.
61.1, 62.4, 69.5, 65.0, 58.2, 67.9, 60.0, 57.7, 64.9, 64.2, 63.2, 62.8, 64.0 63.7
(click me)