A study was conducted in order to estimate μ, the mean number of weekly hours that U.S. adults use computers at home. Suppose a random sample of 81 U.S. adults gives a mean weekly computer usage time of 8.5 hours and that from prior studies, the population standard deviation is assumed to be σ = 3.6 hours.

1. Based on this information, what would be the point estimate for μ?
   
   • 81
   • 8.5
   • 3.6
   • Non of the above.
   
   
   
2. We are 95% confident that the mean number of weekly hours that U.S. adults use computers at home is:
   
   • between 8.1 and 8.9.
   • between 7.8 and 9.2.
   • between 7.7 and 9.3.
   • between 7.5 and 9.5.
   • between 7.3 and 9.7.
   
   
   
3. Which of the following will provide a more informative (i.e., narrower) confidence interval than the one in problem 3?
   
   • (A) Using a sample of size 400 (instead of 81).
   • (B) Using a sample of size 36 (instead of 81).
   • (C) Using a different sample of size 81.
   • (D) Using a 90% level of confidence (instead of 95%).
   • (E) Using a 99% level of confidence (instead of 95%).
   • Both (A) and (D) are correct.
   • Both (A) and (E) are correct.
   
   
   
4. How large a sample of U.S. adults is needed in order to estimate μ with a 95% confidence interval of length 1.2 hours?
   
   • 6
   • 12
   • 20
   • 36
   • 144