Question

Three experiments investigating the relation between need for cognitive closure and persuasion were performed. Part of the study involved administering a "need for closure scale" to a group of students enrolled in an introductory psychology course. The "need for closure scale" has scores ranging from 101 to 201. For the 65 students in the highest quartile of the distribution, the mean score was x = 175.50. Assume a population standard deviation of σ = 7.59. These students were all classified as high on their need for closure. Assume that the 65 students represent a random sample of all students who are classified as high on their need for closure. How large a sample is needed if we wish to be 99% confident that the sample mean score is within 1.9 points of the population mean score for students who are high on the need for closure? (Round your answer up to the nearest whole number.)
students

Anystate Auto Insurance Company took a random sample of 350 insurance claims paid out during a 1-year period. The average claim paid was $1500. Assume σ = $270.

Find a 0.90 confidence interval for the mean claim payment. (Round your answers to two decimal places.)

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Find a 0.99 confidence interval for the mean claim payment. (Round your answers to two decimal places.)

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Coal is carried from a mine in West Virginia to a power plant in New York in hopper cars on a long train. The automatic hopper car loader is set to put 90 tons of coal into each car. The actual weights of coal loaded into each car are normally distributed, with mean μ = 90 tons and standard deviation σ = 0.5 ton.

(a) What is the probability that one car chosen at random will have less than 89.5 tons of coal? (Round your answer to four decimal places.)

(b) What is the probability that 34 cars chosen at random will have a mean load weight x of less than 89.5 tons of coal? (Round your answer to four decimal places.)

Answer 1

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