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Unit 7 Review #2 Name: __________________________ Date: _____________ Section: 7.6 Similar to Exercise: 7.6.5a ___ 1. Suppose that more than a decade ago high levels of lead in the blood put 72% of children at risk. A concerted effort was made to remove lead from the environment. Suppose, according to a survey, only 9% of children in the United States are at risk of high blood-lead levels. In a random sample of 250 children taken more than a decade ago, what is the probability that 160 or more had high bloodlead levels? A) 0.602 B) 0.858 C) 1.000 D) 0.000 E) 0.580 Ans: C Section: 7.1 Similar to Exercise: 7.1.4e ___ 2. True or false: Consider two normal curves. If the first one has a larger mean than the second one, then it also has a larger standard deviation than the second one. A) false B) true Ans: A Section: 7.6 Similar to Exercise: 7.6.10c ___ 3. Suppose that about 66% of the people who are murdered actually knew the person who committed the murder. Suppose that a detective file in Boston has 66 current unsolved murders. What is the probability that fewer than 22 victims did not know their murderer? A) 0.454 B) 0.506 C) 0.494 D) 0.596 E) 0.404 Ans: E Section: 7.2 Similar to Exercise: 7.2.9a ___ 4. Let x = red blood cell (RBC) count in millions per cubic millimeter of whole blood. Suppose for healthy females, x has an approximately normal distribution with mean μ = 4.2 and standard deviation σ = 0.6. Convert the following x interval from a laboratory test to a z interval. A) 2 > z Ans: C B) –4 > z C) 2 < z 5.4 < x D) 3 > z E) 0 < z Section: 7.5 Similar to Exercise: 7.5.6a ___ 5. Suppose x has a distribution with μ = 81 and σ = 9. If random samples of size n = 26 are selected, can we say that the distribution of sample means x for samples of this size is approximately normal? A) yes B) no Ans: B Page 1 Unit 7 Review #2 Section: 7.4 Similar to Exercise: 7.4.2 ___ 6. What is a random sample of size n from a population? A) A random sample of size n from a population is a subset of the population selected in a manner such that every sample of size n which contains the smallest or largest member of the population. B) A random sample of size n from a population is a subset of the population of size n which contains the mean of the population. C) A simple random sample of size n from a population is a subset of the population selected in a manner such that every sample of size n from the population has an equal chance of being selected and every member of the population has an equal chance of being included in the sample. D) A random sample of size n from a population is a set of the population selected in a manner such that every sample of size n containing the median has an equal chance of being selected. E) none of these choices Ans: C Section: 7.5 Similar to Exercise: 7.5.12ai ___ 7. The heights of 18-year-old men are approximately normally distributed with mean 68 inches and standard deviation 3 inches. What is the probability that an 18-year-old man selected at random is greater than 70 inches tall? A) 0.7486 B) 0.2514 C) 0.2486 D) 0.4972 E) 0.5028 Ans: B Section: 7.2 Similar to Exercise: 7.2.6 ___ 8. Raul received a score of 71 on a history test for which the class mean was 61 with standard deviation 10. He received a score of 84 on a biology test for which the class mean was 79 with standard deviation 2.5. On which test did he do better relative to the rest of the class? A) history B) biology Ans: B Section: 7.1 Similar to Exercise: 7.1.2b ___ 9. Look at the normal curve given below, and find σ . A) σ = 25 Ans: E B) σ = 37 C) σ = 33 D) σ = 3 Page 2 E) σ = 4 Unit 7 Review #2 Section: 7.3 Similar to Exercise: 7.3.5 ___ 10. Assume that x has a normal distribution, with the specified mean and standard deviation. Find the indicated probabilities. P (14 ≤ x ≤ 27 ) ; μ = 19; σ = 5 A) 0.726 B) 0.055 C) 0.945 D) 0.787 E) 0.841 Ans: D Section: 7.2 Similar to Exercise: 7.2.8d ___ 11. Suppose a certain species of fawns between 1 and 5 months old have a body weight that is approximately normally distributed with mean μ = 25.6 kilograms and standard deviation σ = 5 kilograms. Let x be the weight of a fawn in kilograms. Convert the following z interval to a x interval. A) x < –44.10 Ans: C B) x > –44.10 –3.7 > z C) x < 7.10 D) x > 44.10 E) x < –7.10 Section: 7.5 Similar to Exercise: 7.5.12bii ___ 12. The heights of 18-year-old men are approximately normally distributed with mean 68 inches and standard deviation 3 inches. What is the probability that the average height x of a sample of ten 18year-old men will be between 67 and 68 inches? A) 0.3531 B) 0.6469 C) 0.1469 D) 0.7062 E) 0.3661 Ans: A Section: 7.3 Similar to Exercise: 7.3.29b ___ 13. A certain company makes 12-volt car batteries. After many years of product testing, the company knows that the average life of a battery is normally distributed, with a mean of 40 months and a standard deviation of 6 months. If the company does not want to make refunds for more than 10% of its batteries under the full-refund guarantee policy, for how long should the company guarantee the batteries (to the nearest month)? A) 47 months B) 43 months C) 32 months D) 40 months E) 28 months Ans: C Section: 7.5 Similar to Exercise: 7.5.1 ___ 14. True or false: The standard error of a sampling distribution is the difference between the mean and the standard deviation. A) true B) false Ans: B Page 3 Unit 7 Review #2 Section: 7.2 Similar to Exercise: 7.2.35 ___ 15. Let z be a random variable with a standard normal distribution. Find the indicated probability below. P ( z ≥ –1) A) 0.841 B) 0.341 C) 0.921 D) 0.171 E) 0.079 Ans: A Page 4