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A medical statistician wants to estimate the average weight loss of people who are on a new diet plan. In a preliminary study, he guesses that the standard deviation of the population of weight loss is about 9 pounds. How large a sample should he take to estimate the mean weight loss to within 3 pounds, with 91% confidence?

1.       Ecommerce.com a large internet retailer is studying the lead time (elapsed time between when an order is placed and when it is filled) for a sample of recent orders. The lead times are reported in days Lead Times (days)                                                            Frequency 0 up to 5                                                                              6 5 up to 10                                                                            7 10 up to 15                                                                          12 15 up to 20                                                                          8 20 up to 25                                                                          7

An urban planner claims that nationally 20% of all families renting condominiums move during the year. A random sample of 200 families renting condominiums in a large development revealed that 28% had moved during the past year. Construct a 90% confidence interval for the population percent of families who moved during the past year.  

The average age for UVU students is 24.6 years, with a standard deviation of 2.8 years.  Assume a normal distribution.  What is the probability of selecting a sample of 200 students with an average age that is less than 24?

Two randomly selected groups of 200 students each were taught two different memorization methods over a four week period. At the end of four weeks a memorization test with a maximum possible score of 100 was given. The confidence interval of the difference in the two group population mean scores on the memorization test was (0.8 to 1.4). What statement best reflects the results of this study?