1. Is it z* or t*? More Practice

2. Confidence Interval Type FormulaConditionsCalculator Means (  known) One sample z- interval 1.Sample is SRS 2.Population is normal or n 30 3.Independent 4. N > 10n ZInterval Means (  unknown) One-sample t- interval 1.Sample is SRS 2.Sample is approx normal (shown graphically) or n 40 3.Independent 4.N > 10n TInterval Confidence Intervals with one sample

3. Example 1 Sulfur compounds cause “off-odors” in wine, so winemakers want to know the odor threshold, the lowest concentration of a compound that the human nose can detect. The odor threshold for dimethyl sulfide (DMS) in trained wine tasters is about 25 micrograms per liter of wine (  ). The untrained noses of consumers may be less sensitive, however. Here are the DMS odor thresholds for 10 untrained students: 3131 43 36 23 34 3230 20 24 Assume that the standard deviation of the odor threshold for untrained noses is known to be  = 7.

4. Construct and interpret a 93% confidence interval for the mean DMS odor threshold among all untrained students. Determine the sample size you would need to estimate µ within 0.02 at a 93% confidence level.

5. Example 2 National Fuelsaver Corporation manufactures the Platinum Gasaver, a device they claim “may increase gas mileage by 22%.” Here are the percent changes in gas mileage for 15 identical vehicles, as presented in one of the company’s advertisements: 48.3 46.9 46.8 44.6 40.2 38.5 34.6 33.7 28.7 28.7 24.8 10.8 10.4 6.9 12.4 Construct and interpret a 90% confidence interval to estimate the mean fuel savings in the population of all such vehicles.

6. Example 3 An asbestos removal company places great importance on the safety of their employees. The protective suits that the employees wear are designed to keep asbestos particles off the employees body. The owner is interested in knowing the average amount of asbestos particles left on the employee’s skin after a days work. A random sample of 200 employees had skin tests after removing their protective suit. The average number of particles found was.481 particles per square centimeter. Assuming that the population standard deviation is 0.35 particles per square centimeter, calculate a 95% confidence interval for the number of particles left on the employee’s skin.

7. Example 4 A biology student at a major university is writing a report about bird watchers. She has developed a test that will score the abilities of bird watchers to identify common birds. She collects data from a random sample of people that classify themselves as bird watchers (data shown below). Find a 90% confidence interval for the mean score of the population of bird watchers.

8. Example 5 You measure the weights of 24 male runners. You do not actually choose an SRS, but you are willing to assume that these runners are a random sample from the population of male runners in your town. Here are their weights in kilograms: 67.8 61.9 63.0 53.1 62.359.755.4 58.967.8 61.9 63.0 53.1 62.359.755.4 58.9 60.9 69.2 63.7 68.3 64.765.656.057.860.9 69.2 63.7 68.3 64.765.656.057.8 66.0 62.9 53.6 65.0 55.860.469.361.766.0 62.9 53.6 65.0 55.860.469.361.7