document.write( "Question 1151477: Scores on a certain exam are normally distributed with a mean of 90 and a variance of 25. What is the z-value for a score of 80?
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Algebra.Com's Answer #773238 by rothauserc(4718) $\"\"$ $\"About$

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z-score formula is defined as
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\n" ); document.write( "z-score = (X - mean)/standard deviation
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\n" ); document.write( "standard deviation = square root of variance, for this problem
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\n" ); document.write( "standard deviation = square root(25) = 5
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\n" ); document.write( "z-score = (80 - 90)/5 = -2
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\n" ); document.write( "Note to find the probability associated with this z-score, you lookup the z-score in the table of z-scores
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\n" ); document.write( "If your table of z-scores is only for positive values, then lookup the probability associated with, in this case, 2. Then subtract that value from 1 to get the probability associated with -2
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\n" ); document.write( "Why do you think this works?
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