MS 150 Statistics Quiz 07 Fall 2003 8.1 • Name: _______________

Over a sample size n of 30 weeks the cafeteria found that they have been using a sample mean x of 22.5 bags of rice per week with a sample standard deviation sx of 2.5. Construct a 95% confidence interval for the population mean number of rice bags.

1. _______ Write down the sample size n.
2. _______ Is the sample size n greater than or equal to 30?
3. _______ Write down the sample sample mean x.
4. _______ Write down the sample standard deviation sx.
5. _______ Write down the confidence level c.
6. Use the information above to sketch the 95% confidence interval:

7. _______ Determine the area in both tails.
8. _______ Determine the area in the left tail.
9. _______ Determine the left -zc value.
10. _______ Write down the right zc value.
11. _______ Determine the error E.
12. _______ Determine the left (lower) bound for the population mean µ.
13. _______ Determine the right (upper) bound for the population mean µ.
14. The confidence interval for the population mean number of rice bags µ is:
_________ < µ < _________
Confidence interval statistics
Find a zc value from a confidence level c zc   =ABS(NORMSINV((1-c)/2))
Calculate an error tolerance E of a mean for n >= 30 using sx E =zc*sx/SQRT(n)
Calculate a confidence interval for a population mean µ from a sample mean x and an error tolerance E   x-E<= µ <=x+E