SOLUTION: The lifetime cellphone batteries from a certain manufacturer is 25 hours if used continuously, the standard deviation is 5 hours. If the distribution is normally distributed, how m

Algebra ->  Probability-and-statistics -> SOLUTION: The lifetime cellphone batteries from a certain manufacturer is 25 hours if used continuously, the standard deviation is 5 hours. If the distribution is normally distributed, how m      Log On


   

Question 1081965: The lifetime cellphone batteries from a certain manufacturer is 25 hours if used continuously, the standard deviation is 5 hours. If the distribution is normally distributed, how many hours is the cut-off in selecting the best 10% in terms of lifetime?
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
z0.90=1.28
1.28=(x-25)/5; z values=(x-mean)/sd
x-25=6.4
x=31.4 hours