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Unformatted text preview: Insert Function: NORMSINV(0.9) or NORMINV(0.9, 0, 1) Both these functions return the answer z0 = 1.2816 26 Chapter 6 Example: student textbook buying exercise Continued (e) Find a range of dollar spending on textbooks that includes 80% of all students. Any number of ranges can be found. That is, a variety of values x 0 and x 1 with x 0 <380 and x 1 >380 will satisfy: P(x 0 < X < x 1 ) = 0.80 The shortest range is centered at the mean $380. To calculate this range, find a number a such that: P(380 − a < X < 380 + a ) = 0.80 This is illustrated with a graph: 2 PDF of X ~ N( 380 , 50 ) f(x) Area = 0.80 Lower Tail Area = 0.10 380a Upper Tail Area = 0.10 380
x 27 380+a Chapter 6 By inspe...
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This note was uploaded on 02/06/2014 for the course ECON ECON 325 taught by Professor Whistler during the Spring '10 term at The University of British Columbia.
 Spring '10
 WHISTLER

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