document.write( "Question 871441: Good evening guys, I need help with this question, thank you in advance!!!\r \n" );
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document.write( "A study has shown that 20% of all college textbooks cost at least $70. It is known that the standard deviation of the prices of the college textbook is $9.50. Assuming that prices of all college textbooks follows a normal distribution; find the mean price of all college textbooks.\r \n" );
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document.write( "This is what I did so far.\r \n" );
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document.write( "x= cost of textbook x~normal (M, SD= 9.50)\r \n" );
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document.write( "P(x>70)=20%\r \n" );
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document.write( "P(x<70)=80%\r \n" );
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document.write( "P(z<70-M)=.8000 \n" );
document.write( "------- \n" );
document.write( " 9.50 \n" );
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