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    Statistics: Sampling Distribution and Estimation

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    8.46 A random sample of 10 miniature Tootsie Rolls was taken from a bag. Each piece was weighed on a very accurate scale. The results in grams were
    3.087 3.131 3.241 3.241 3.270 3.353 3.400 3.411 3.437 3.477

    (a) Construct a 90 percent confidence interval for the true mean weight.
    (b) What sample size would be necessary to estimate the true weight with an error of +/- 0.03 grams with 90 percent confidence?
    (c) Discuss the factors which might cause variation in the weight of Tootsie Rolls during manufacture. (Data are from a project by MBA student Henry Scussel.)

    8.62 In 1992, the FAA conducted 86,991 pre-employment drug tests on job applicants who were to be engaged in safety and security-related jobs, and found that 1,143 were positive. (a) Construct a 95 percent confidence interval for the population proportion of positive drug tests. (b) Why is the normality assumption not a problem, despite the very small value of p? (Data are from Flying 120, no. 11 [November 1993], p. 31.)

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