A school social worker wishes to estimate the mean amount of time each week that high school students spend with friends. She obtains a random sample of 520 high school students and finds that the mean weekly time spent with friends is 11.6 hours. The population standard deviation amount of time spent with friends is 4.2 hours. What is the lower bound for a 90% confidence interval for the true mean hours students spend with friends? (Round your answer to three decimal places.)

When forming a confidence interval for matched-pair data the point estimate is the Select one: O A. standard deviation of the differences. OB. differences of the standard deviations. O C. mean of the differences. O D. difference of the means.

In a survey, 21 people were asked how much they spent on their child's last birthday gift. The results were roughly bell-shaped with a mean of $30.9 and standard deviation of $12.7. Estimate how much a typical parent would spend on their child's birthday gift (use a 90% confidence level). Give your answers to 3 decimal places. Express your answer in the format of a + E. $ 30.9 V + $ 4.770

A successful basketball player has a height of 6 feet 11 ​inches, or 211 cm. Based on statistics from a data​ set, his height converts to the z score of 5.17. How many standard deviations is his height above the​ mean?

A professor was curious about her students' grade point averages. She took a random sample of 15 students and found a mean GPA of 3.01 with a standard deviation of 0.534. Which of the following formulas gives a 99% confidence interval for the mean GPA of the professor's students?

A survey of 32,782 adults in 2004 indicated that 24.6% of adults were current smokers. A similar study conducted in 1995 of 40,000 adults indicated that 29.7% were current smokers. a. Find and interpret a point estimate of the difference between the proportion of current smokers in 1995, and the proportion of current smokers in 2004. b. A 95% confidence interval for the true difference is (-0.058,-0.045). Interpret. c. What assumptions must you make for the confidence interval i part b to be valid? (…) a. Find a point estimate of the difference between the proportion of current smokers in 1995 and the proportion of current smokers in 2004. (Round to three decimal places as needed.)

a researcher wishes to develop an interval estimate for response scores on user surveys. She's not sure about the standard deviation, but in previous years the scores have ranged from 25 to 86. How large a sample should she draw if she wants to construct a 95% confidence interval level that will be within 3 points of the population mean score?

Use z scores to compare the given values. The tallest living man at one time had a height of 252 cm. The shortest living man at that time had a height of 53.2 cm. Heights of men at that time had a mean of 172.68 cm and a standard deviation of 8.46 cm. Which of these two men had the height that was more extreme? see score past due Since the z score for the tallest man is z=] and the z score for the shortest man is z= the height that was more extreme. (Round to two decimal places.)

The following is the number of hours of sleep obtained by eight college freshmen.  Use the data to find a 92% confidence interval for the true mean number of hours of sleep by college freshmen. ​​7.5​    8.0​   6.5​  24​  8.5​  6.5​  7.0​   7.5