In a mid-size company, the distribution of the number of phone calls answered each day by each of the 12 receptionists is bell-shaped and has a mean of 50 and a standard deviation of 10. Using the empirical rule (as presented in the book), what is the approximate percentage of daily phone calls numbering between 30 and 70?

The survey of study habits and attitudes (ssha) is a psychological test that measures the motivation, attitude toward school, and study habits of students, scores range from 0 to 200. the mean score for u.s. college students is about 115, and the standard deviation is about 30. a teacher who suspects that older students have better attitudes toward school gives the ssha to 55 students who are at least 30 years of age. the mean score is 113.2. assume the population standard deviation is 30 for older students what is the margin of error for a 95% confidence interval for the population mean score for a. older students? b. compute the 95% confidence interval for the population mean score for older students. c. compute the 99% confidence interval for the population mean score for older students. d. compute the 88% confidence interval for the population mean score for older students.

To keep cylindrical tanks from tipping over, a designer is planning to enlarge the original area of the base by 50%. the new tank should have the same volume as the original. how should the designer change the height of the tank? a: make it 50% taller than the height of the original tank. b: make it 6623% taller than the height of the original tank c: make it 3313% shorter than the height of the original tank d: make it 50% shorter than the height of the original tank.

Kari plans to sample 20 people of a population that contains 100 students. she wants to determine how many people wake up before 6 a.m. which sample is the most random?