答案和详解如下： Q4. The owner of a bowling alley determined that the average weight for a bowling ball is 12 pounds with a standard deviation of 1.5 pounds. A ball denoted “heavy” should be one of the top 2% based on weight. Assuming the weights of bowling balls are normally distributed, at what weight (in pounds) should the “heavy” designation be used? A) 15.08 pounds.
B) 14.22 pounds.
C) 14.00 pounds.
Correct answer is A) The first step is to determine the z-score that corresponds to the top 2%. Since we are only concerned with the top 2%, we only consider the right hand of the normal distribution. Looking on the cumulative table for 0.9800 (or close to it) we find a z-score of 2.05. To answer the question, we need to use the normal distribution given: 98 percentile = sample mean + (z-score)(standard deviation) = 12 + 2.05(1.5) = 15.08. Q5. Which of the following represents the mean, standard deviation, and variance of a standard normal distribution? A) 0, 1, 1. B) 1, 1, 1. C) 1, 2, 4. Correct answer is A) By definition, for the standard normal distribution, the mean, standard deviation, and variance are 0, 1, 1. Q6. Standardizing a normally distributed random variable requires the: A) mean, variance and skewness. B) mean and the standard deviation. C) natural logarithm of X. Correct answer is B) All that is necessary is to know the mean and the variance. Subtracting the mean from the random variable and dividing the difference by the standard deviation standardizes the variable. | 
发表于 2009-1-9 10:33
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