Q7b

1. What is the X2 left value for a 95% confidence interval when the sample size is 12?

2. The actual arrival times of 10 randomly selected flights of KLM Airlines were checked against the posted arrival times. The sample had a variance of 26.50 minutes. What is the 98% confidence interval for the true variance of all arrival times?

3. VISA reported with 95% confidence that 19% of those surveyed used checks to pay for purchases. If 1478 people participated in the survey, what was the percentage of error?

4. A poll of 1000 people reported that 42% expect to win the lottery(yeah right!!!). What is the 99% confidence interval of the true proportion of people who expect not to win the lottery?(Assume that all who participated in the survey responded with either they did expect to win the lottery or not win the lottery.)

5. A political candidate wants to estimate his chances of winning the coming election for mayor by conducting a survey. The margin of error is to be 2% with 99% confidence. What is the minimum sample size necessary?

6. What is the value for X2 right for a 95% confidence interval when n = 24?

7. At a one-hour PhasterPhoto film developing store in downtown Denver, 12 randomly selected people were asked how long it took to get their films developed. The number of minutes required for processing are listed below.

25

30

41

36

45

18

33

52

39

43

28

20

What is the 98% confidence interval for the standard deviation of all processing times?

1. A poll of 600 frequent airline travelers found that 60% really like the food on their flights. What is the 95% confidence interval for the true proportion of airline travelers who really like the food on their flights?

2. A selection of 16 milk products were measured for grams of fat. The standard deviation of this sample was 2.98 grams. What is the 95% confidence interval for the standard deviation of fat grams in milk products?

3. A quality control expert wants to estimate the proportion of defective computer keyboards that are being manufactured by her company to within 3.5%. Based on a previous sample that showed 20 defects out of 400, how large a sample is needed to estimate the true proportion of defective components at a 99% level of confidence?