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Unformatted text preview: Normal Distribution 9.) The mean of a normal probability distribution is 500; the standard deviation is 10. a.) About 68 percent of the observations lie between what two values? 490, 510 500 1(10) = 490 500 + 1(10) = 510 b.) About 95 percent of the observations lie between what two values? 480, 520 500 2(10) = 480 500 + 2(10) = 520 c.) Practically all of the observations lie between what two values? 470, 530 500 3(10) = 470 500 + 3(10) = 530 19.) According to the Internal Revenue Service, the mean tax refund for the year 2007 was $2,708. Assume the standard deviation is $650 and that the amounts refunded follow a normal probability distribution. a.) What percent of the refunds are more than $3,000? .3264 3000 2708 / 650 = .45 z = 0.1736 .5000  .1736 = .3264 b.) What percent of the refunds are more than $3,000 but less than $3,500? .2152 3000 2708 / 650 = .45 z = .1736 3500 2708 / 650 = 1.22 z = .3888 .3888  .1736 = .2152 c.) What percent of the refunds are more than $2,500 but less than $3,500? .5143 2500 2708 / 650 = .32 z= .1255 3500 2708 / 650 = 1.22 z=. 3888 .3888 + .1255 = .5143 22.) Among U.S. cities with a population of more than 250,000 the mean oneway commute to work is 24.3 minutes. The longest oneway travel time is New York City, where the mean time is 38.3 minutes. Assume the distribution of travel times in New York City follows the normal probability distribution and the standard deviation is 7.5 York City follows the normal probability distribution and the standard deviation is 7....
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This note was uploaded on 10/15/2009 for the course ECON 2302 taught by Professor Parker during the Spring '09 term at University of TexasTyler.
 Spring '09
 Parker

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