document.write( "Question 431251: I am having trouble with this: I want to understand how to find the standard deviation given average age of cars 19.4 years, there is normal distribution, 20% cars
\n" ); document.write( "are older than 22.8 years find standard deviation \n" ); document.write( "

Algebra.Com's Answer #299362 by Edwin McCravy(20056) $\"\"$ $\"About$

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document.write( "P(z > ) = .20\r\n" );
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document.write( "P(z > ) = .20\r\n" );
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document.write( "Next we find the z-score which has .20 of the area to\r\n" );
document.write( "the right of it.\r\n" );
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document.write( "It will therefore have .5-.20 or .30 of the area between the\r\n" );
document.write( "center line and the z-score.\r\n" );
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document.write( "So you will look through the body of your table until\r\n" );
document.write( "you find the closest entry to .30.\r\n" );
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document.write( "The closest entry to .30 is .2995, which corresponds to\r\n" );
document.write( "the z-score of 0.84\r\n" );
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document.write( "[Some books have a normal table that gives values from\r\n" );
document.write( "the extreme left side. In that case you will look for\r\n" );
document.write( "the closest value to .80 and that will be 0.7995, and\r\n" );
document.write( "that will also correspond to the z-score of 0.84].\r\n" );
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document.write( "So Solve this equation for :\r\n" );
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document.write( "Solve that and get \r\n" );
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document.write( "Edwin

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