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A doctor wants to know if a blood pressure medication is effective. Six subjects have their blood pressures recorded. After twelve weeks on the medication, the same six subjects have their blood pressure recorded again. For this test, only systolic pressure is of concern. Test at the 1% significance level. Patient A B C D E  F Before 161 162 165 162 166 171 After 158 159 166 160 167 169
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Two types of phone operating system are being tested to determine if there is a difference in the proportions of system failures (crashes). Fifteen out of a random sample of 150 phones with OS1 had system failures within the first eight hours of operation. Nine out of another random sample of 150 phones with OS2 had system failures within the first eight hours of operation. OS2 is believed to be more stable (have fewer crashes) than OS1. Test appropriate hypothesis.
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Variability in the return of traded security is often thought as a measure of "total risk of the security. A certain portfolio manager will only invest in a security if its population standard deviation of return does not exceed 10% per month. A sample of 18 monthly returns on a particular security yielded a sample deviation of 14.2% per month. Construct a 90% confidence interval estimate for the population variance.
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According to the National Traffic Safety Council of Namibia, the probability that a traffic fatality will involve an intoxicated or alcohol-impaired driver is 40%. If eight traffic fatalities observed last month. a. Find the probability that the number of an intoxicated or alcohol-impaired driver is exactly three. b. Find the expected value and standard deviation of the number of intoxicated or alcohol-impaired drivers.
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A national bank analysed a random sample of 365 cheque accounts at their Windhoek branch and found that 78 of them were overdrawn. Estimate, with 90% confidence, the proportion of all bank accounts at the Windhoek branch of the bank that were not overdrawn.
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A researcher wishes to estimate, with 99% confidence, the population proportion of adults who are confident with their country's banking system. His estimate must be accurate within 2% of the population proportion. (a) No preliminary estimate is available. Find the minimum sample size needed. (b) Find the minimum sample size needed, using a prior study that found that 25% of the respondents said they are confident with their country's banking system.
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Two business schools, A and B, located in the same metropolitan area and they are competing for bragging rights. One of the points of competition is average salary of graduating seniors. 30 graduating seniors from A and 25 from B were surveyed. A’s students had an average salary of \$62,000, and B's students had an average salary of \$67,000. Based on historical data, the population standard deviation is assumed to be \$10,000 for A and \$15,000 for B. Construct the hypotheses and conduct the appropriate tests that school B could use to claim that its students have a higher average graduating salary that A. Using a 5% level of significance, and the sample data provided, determine if school B can claim that its average graduating salary is greater than that of school A.
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A researcher claims that average body temperature is different for the two genders. A sample of 65 men and 65 women yields average body temperatures of 98.105 and 98.394 oF, respectively. Based on historical data, the standard deviation of body temperature is known to be 0.699 and 0.743 degrees Fahrenheit, respectively. At a 5% level of significance, can you conclude that average body temperature differs with gender? Would your answer change for a 1% level of significance?
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The table below summarizes results from a study of people who refused to answer survey questions. Use the table to answer the following questions. Be very careful to read the question carefully to determine whether or not there is overlap. Age  18-21  22-29   30-39  40-49  50-59  60 and over Responded  70  252  242  133  135  199 Refused  13  22  35  28  37  59 If one of the subjects is randomly selected, what is the probability that a randomly selected person is between 22 and 29 years or refused to answer? The probability that a randomly selected person is between 22 and 29 years or refused to answer is _____ (Do not round until the final answer. Then round to three decimal places as needed. If one of the subjects is randomly selected, what is the probability that the selected person was between 16 and 21 years or refused to answer? The probability that the selected person was between 18
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The lengths of paper clips produced by a factory are normally distributed with a mean of 2.52 cm and a standard deviation of 0.08 cm. (a) What is the probability that a paper clip selected at random will have a length more than 2.55 cm? (b) If 3% of the paper clips produced had a length of more than k cm, find the value of k.
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