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Unformatted text preview: 1. Find the critical value zc necessary to form a confidence interval at the given level of confidence. (References: definition for level of confidence page 311, end of section exercises 5 – 8 page 317) (2.5 points each) a. 90% 1 sided confidence interval: z = 1.282 b. 80% 1 sided confidence interval: z = 0.842 2. The new Twinkle bulb has a standard deviation hours. A random sample of 50 light bulbs is selected from inventory. The sample mean was found to be 550 hours. a. Find the margin of er or E for a 90% confidence interval. (5 points) Round your answer to the nearest hundredths. . (References: definition of margin of er or on page 312 and example 2 on page 312). The standard deviation is not given, but necessary to answer this question. Some people use the z-distribution here instead of the more appropriate t-distribution, in which case you should replace 1.677 with 1.645. b. Construct a 90% confidence interval for the mean life, ? of al Twinkle bulbs. (5 points) (References: example 5 page 315, end of section exercises 51 - 56 pages 319 - 320) b....
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This note was uploaded on 11/07/2011 for the course ACC 220 taught by Professor - during the Spring '10 term at University of Phoenix.
- Spring '10