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PRINTABLE VERSION Test 2 You scored 21 out of 49 Question 1 Your answer is CORRECT. An electrical firm manufactures light bulbs that have a length of life that is approximately normally distributed with a standard deviation of 60 hours. How large a sample is need if we wish to be 94% confident that we will be within 10 hours of the true mean? a) 12 b) 85 c) 143 d) 128 e) 24 f) None of the above. Question 2 Your answer is INCORRECT. A __________ error consists of rejecting the null hypothesis H 0 when H 0 is true. a) Type I b) Type II c) Power Question 3 Your answer is CORRECT. The average life a manufacturer's blender is 5 years, with a standard deviation of 1 year. Assuming that the lives of these blenders follow approximately a normal distribution, find the probability that the mean life a random sample of 25 such blenders falls between 4.7 and 5.1 years.

a) 0.3085 b) 0.1577 c) 0.6247 d) 0.3753 e) 0.6915 f) None of the above. Question 4 Your answer is CORRECT. What will reduce the width of a confidence interval? a) Decrese confidence level. b) Increase confidence level. c) Increase variance. d) Decrease the number in sample. Question 5 Your answer is INCORRECT. A sample of 31 boxes of cereal has a sample standard deviation of 0.81 ounces. Construct a 96% confidence interval to estimate the true standard deviation of the filling process for the boxes of cereal. a) (0.410, 1.207) b) (0.712, 0.712) c) (0.525, 1.095) d) (0.641, 1.099) e) None of the above. Question 6

e) (0.651, 0.321) Question 8 Your answer is CORRECT. This is a written question, worth 17 points. DO NOT place the problem code on the answer sheet. A proctor will fill this out after exam submission. Show all steps (work) on your answer sheet for full credit. Problem Code: 772 Suppose the random variable has CDF given by the function Part a: Find . Part b: Find the desity function . Part c: Find . Part d: Find the variance of . Part e: Find the median of . a) I have placed my work and my answer on my answer sheet. b) I want to have points deducted from my test for not working this problem. Question 9 Your answer is CORRECT. This is a written question, worth 17 points. DO NOT place the problem code on the answer sheet. A proctor will fill this out after exam submission. Show all steps (work) on your answer sheet for full credit. Problem Code: 924 A study of iron deficiency in infants compared samples of infants whose mothers chose different ways of feeding them. One group contained breast-fed infants. The children in another group were fed a standard baby formula without any iron supplements. Here are summary results on blood hemoglobin levels at 12 months of age: Group n x s Breast-fed 23 15.3 2.2 Formula 31 16.9 1.8 X F(x) = ⎧ ⎩ ⎨ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ 0 1 8 x 3 1 x < 0 0 ≤ x ≤ 2 x > 2 P(1 ≤ X ≤ 1.5) f(x) E[X] X X

Part a : We want to see if the mean hemoglobin level is greater among formula-fed babies. State the hypotheses. Part b : Perform the significance test on your hypothesis. Report the test statistic and p-value. State your conclusion in terms of the issue. Part c : Give a 95% confidence interval for the mean difference in hemoglobin level between the two populations of infants. a) I have placed my work and my answer on my answer sheet. b) I want to have points deducted from my test for not working this problem. Question 10 Your answer is CORRECT. This is a written question, worth 17 points. DO NOT place the problem code on the answer sheet. A proctor will fill this out after exam submission. Show all steps (work) on your answer sheet for full credit. Problem Code: 1012 The belief is that the mean number of hours per week of part-time work of high school seniors in a city is 10.5 hours. Data from a simple random sample of 22 seniors indicated that their mean number of part-time work was 12.3 with a standard deviation of 1.3. Test whether these data cast doubt on the current belief. (use α = 0.05) Part a : State your null and alternative hypotheses. Part b : Sketch the rejection region. Part c : Calculate the test statistic. Plot this value in your sketch in part b. Part d : Determine the P-value for your test. Part e : State your conclusions clearly in complete sentences. a) I have placed my work and my answer on my answer sheet. b) I want to have points deducted from my test for not working this problem.