1. A civil engineer is analyzing the compressive strength of concrete. Compressive strength is normally

distributed with 2 = 1000(psi)2. A random sample of 12 specimens has a mean compressive strength

of = 3250 psi.

(a) Construct a 95% two-sided confidence interval on mean compressive strength.

(b) Construct a 99% two-sided confidence interval on mean compressive strength.

2. A research engineer for a tire manufacturer is investigating tire life for a new rubber compound and

has built 16 tires and tested them to end-of-life in a road test. The sample mean and standard

deviation are 60,139.7 and 3645.94 kilometers. Find a 95% confidence interval on mean tire life.

3. The fraction of defective integrated circuits produced in a photolithography process is being

studied. A random sample of 300 circuits is tested, revealing 13 defectives.

(a) Calculate a 95% two-sided CI on the fraction of defective circuits produced by this particular tool.

4. Consider the tire-testing data described in Number 2. Compute a 95% prediction interval on the life

of the next tire of this type tested under conditions that are similar to those employed in the original

test.

5. Consider the tire-testing data in Number 2. Compute a 95% tolerance interval on the life of the tires

that has confidence level 95%. Compare the length of the tolerance interval with the length of the

95% CI on the population mean.

6. The Bureau of Meteorology of the Australian Government provided the mean annual rainfall (in

millimeters) in Australia 1983-2002 as follows (http://www.bom.gov.au/climate/change/rain03.txt):

499.2, 555.2, 398.8, 391.9, 453.4, 459.8, 483.7, 417.6, 469.2, 452.4, 499.3, 340.6, 522.8, 469.9, 527.2,

565.5, 584.1, 727.3, 558.6, 338.6

Check the assumption of normality in the population. Construct a 95% confidence interval for the

mean annual rainfall.

7. The 2004 presidential election exit polls from the critical state of Ohio provided the following

results. The exit polls had 2020 respondents, 768 of whom were college graduates. Of the college

graduates, 412 voted for George Bush.

(a) Calculate a 95% confidence interval for the proportion of college graduates in Ohio who voted for

George Bush.

8. A post mix beverage machine is adjusted to release a certain amount of syrup into a chamber where

it is mixed with carbonated water. A random sample of 25 beverages was found to have a mean syrup

content of x = 1.10 fluid ounce and a standard deviation of s = 0.015 fluid ounce. Compute a 95%

prediction interval on the syrup volume in the next beverage dispensed.

9. Consider the syrup-volume data in number 8. Compute a 95% tolerance interval on the syrup

volume that has confidence level 90%.