SOLUTION: birth weights in the united states have a distribution that is approximately normal with a mean of 3369 g and a standard deviation of 574 g. A. find the birth weight that is the

Question 1091259: birth weights in the united states have a distribution that is approximately normal with a mean of 3369 g and a standard deviation of 574 g.
A. find the birth weight that is the cutoff between the bottom 10% and the top 90%
B. 25 babies are randomly selected, find the probability that their mean birthweight is greater than 3400 g
Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
the 10% percentile is at z=-1.28
the 90th percentile is at z=+1.28
multiply that by the sd and add to mean to get 90% cut off and subtract to get 10% cut off
574*1.28=734.7, round to 735
(2634, 4104) units are gm.
the mean greater than 3400 is
z>(3400-3369)/574/sqrt (25)
z>155/574
z>0.2700
That probability is 0.3936.
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