SOLUTION: Good evening guys, I need help with this question, thank you in advance!!! A study has shown that 20% of all college textbooks cost at least $70. It is known that the standard d

Question 871441: Good evening guys, I need help with this question, thank you in advance!!!
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.
This is what I did so far.
x= cost of textbook x~normal (M, SD= 9.50)
P(x>70)=20%
P(x<70)=80%
P(z<70-M)=.8000
-------
9.50
Answer by Yzeph(21) (Show Source): You can put this solution on YOUR website!

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