Facebook: A study showed that two years ago, the mean time spent per visit to Facebook was 20.8 minutes. Assume the standard deviation is a=8.0 minutes. Suppose that a simple random sample of 107 visits was selected this year and has a sample mean of x= 18.8 minutes. A social scientist is interested to know whether the mean time of Facebook visits has decreased. Use the a=0.10 level of significance and the critical value methad with the table. (a) State the appropriate null and alternate hypotheses. (b) Compute the value of the test statistic. (c) State a conclusion. Use the a = 0.10 level of significance.

In a school district, all sixth grade students take the same standardized test. The superintendant of the school district takes a random sample of 30 scores from all of the students who took the test. She sees that the mean score is 169 with a standard deviation of 7.0674. The superintendant wants to know if the standard deviation has changed this year. Previously, the population standard deviation was 13. Is there evidence that the standard deviation of test scores has decreased at the α=0.005 level? Assume the population is normally distributed. Step 4: Make a decision. Is it reject Null hypothesis or Fail to reject Null hypothesis? Step 5: What is the conclusion? Is there sufficient evidence or there is not sufficient evidence to show that the standard deviation of the test scores has decreased?

The heart rate of 20 patients in the ICU have a mean of 95.3 beats per minute and a standard deviation of 19.6 beats per minute. Are heart rates from the ICU patients unusual given a normal heart rate has a mean of 72 beats per minute? What is the t-stastic?

An article in the San Jose Mercury News stated that students in the California state universitysystem take 4.25 years, on average, to finish their undergraduate degrees. Suppose you believe that the mean time is longer. You conduct a survey of 64 students and obtain a sample mean of 4.5 with a sample standard deviation of 1.5. Do the data support your claim at the 1% level?

The common fruit fly Drosophila melanogaster is the most studied organism in genetic research because it is small, is easy to grow, and reproduces rapidly. The length of the thorax (where the wings and legs attach) in a population of male fruit flies is approximately Normal with mean 0.800 millimeters (mm) and standard deviation 0.078 mm. Use software or Table A. (a) What proportion of flies have thorax length less than 0.66 mm? (Enter your answer as a percentage rounded to two decimal places.) 6.18 proportion: Incorrect (b) What proportion of flies have thorax length greater than 0.93 mm? (Enter your answer as a percentage rounded to two decimal places.) 18.41 proportion: Incorrect

An analyst found that the average amount of money in bank accounts at his/her bank is $2,000 with a standard deviation of $150.  What would be the variance?

In a random sample of 6 cell phones, the mean full retail price was 517.30 and standard deviation is 184.00. Further research suggests that the population mean is 425.73. Does the t-value for the original sample fall between -t0.99 and t0.99?