HW9_skeleton

9.2

• 1. Decreases
• 2. False. The t-distribution is centered at 0 and is symmetric about 0.
• 3. Alpha
• 4. True. Since t-sub 0.10 with 5 degrees of freed = 1.476 > t-sub 0.10 with 10 degrees of freedom = 1.372.
• 5. False. The sample size can be large.
• 6. Robust
• 1. t sub 0.10 = 1.316

  2. t sub 0.05 = 1.697

  3. t sub 0.01 = 2.552

  4. t sub 0.05 = 1.725

• 1. t sub 0.02 = 2.205

  2. t sub 0.10 = 1.31

  3. t sub 0.05 = 1.943

  4. t sub 0.025 = 2.120

• 13. x-bar = 18+24/2 = 21
• 14. point estimate = 25 margin of error = 5
• 1. t sub 0.02 = 2.172 Lower bound = 103.66 Upper bound = 112.33

  2. t sub 0.02 = 2.398 Lower bound = 100.42 Upper bound = 115.58

  3. t sub 0.05 = 1.711 Lower bound = 104.58 Upper bound = 115.58

  Decreasing the confidence level decreases the margin of error.

  4. No because the sample sizes are too small.
• 1. This statement is flawed because this interpreation implies that the population mean varies rather than the interval.

  2. This statement is correct because an interval has beeen provided for the population mean

  3. This statement is flawed because this interpretation makes an implication about the individuals rather than the mean.

  4. This statement is flawed because the interpretations should be about the mean numbers of hours worked by the adult Americans, not about adults in Idaho.

• 29. T sub 0.025 = 1.987 Lower bound = 317.63 Upper bound = 394.57

  We are 95% confident that the mean number of licks to the center of a tootsie pop is between 317.63 and 394.57.

• 30. Lower bound = 12.05 Upper bound = 14.75

  We are 95% confident that the mean number of books read by Americans in the past year was between 12.05 and 14.75

9.3

• 1. False. The chi-square distribution is skewed to the right.
• 2. True.
• 3. False. to contruct a confidence interval about a population variance or standard deviation, the sample must come froma normally distributed population.
• 4. False.
• 5. Chi-Square sub 0.95 = 10.117 Chi-Square sub 0.05 = 30.144
• 6. Chi-square sub 0.975 = 12.4 (rounded) Chi-square sub 0.025 = 39.4 (rounded)
• 1. Chi-Square sub 0.95 = 10.117 Chi-Square sub 0.05 = 30.144 Lower Bound = 7.94 Upper Bound = 23.66

  2. Chi-square sub 0.95 = 17.708 Chi-square sub 0.05 = 42.557 Lower Bound = 8.59 Upper Bound = 20.63

  3. Chi-square sub 0.99 = 7.633 Chi-square sub 0.01 = 36.191 Lower Bound = 6.61 Upper Bound = 31.36

• 11. s-square = 0.102, Chi-square sub 0.975 = 3.816 Chi-sqaure sub 0.025 = 21.920 Lower Bound = 0.226 Upper Bound = 0.542
  We can be 95% confident that the population standard deviation of the pH of rainwater in Tucker County, West Virginia is between 0.226 and 0.542.