答案和详解如下： Q1. The average annual rainfall amount in Yucutat, Alaska, is normally distributed with a mean of 150 inches and a standard deviation of 20 inches. The 90% confidence interval for the annual rainfall in Yucutat is closest to: A) 117 to 183 inches. B) 110 to 190 inches. C) 137 to 163 inches. Correct answer is A) The 90% confidence interval is µ ± 1.65 standard deviations. 150 − 1.65(20) = 117 and 150 + 1.65(20) = 183. Q2. The standard normal distribution is most completely described as a: A) distribution that exhibits zero skewness and no excess kurtosis. B) symmetrical distribution with a mean equal to its median. C) normal distribution with a mean of zero and a standard deviation of one. Correct answer is C) The standard normal distribution is defined as a normal distribution that has a mean of zero and a standard deviation of one. The other choices apply to any normal distribution. Q3. Monthly sales of hot water heaters are approximately normally distributed with a mean of 21 and a standard deviation of 5. What is the probabilility of selling 12 hot water heaters or less next month? A) 3.59%. B) 1.80%. C) 96.41%. Correct answer is A) Z = (12 – 21) / 5 = -1.8 From the cumulative z-table, the probability of being more than 1.8 standard deviations below the mean, probability x < -1.8, is 3.59%. | 
发表于 2009-1-9 10:31
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