SOLUTION: the length of all human pregnancies is approximately normal with a mean of 266 days and a standard deviation of 16 days , a) if 20 pregnancies are selected at random, what is the p

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Question 851710: the length of all human pregnancies is approximately normal with a mean of 266 days and a standard deviation of 16 days , a) if 20 pregnancies are selected at random, what is the probability that the sample average is less than 260 days? b)if 20 pregnancies are selected at random, what is the probability that the sample mean is within 5 days of the population mean?
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
 

Hi,

mean of 266 days and a standard deviation of 16

Sample of 20,  SD of population = 16/sqrt(20) = 3.5777

 z+=+%28260-+266%29%2F3.5777+=+-6%2F3.5777+= -1.6771 

NORMSDIST(-1.6771)= .0476  0r 4.76%

P(-5/3.5777 ≤ z ≤ 5/3.5777) = P(-1.3975 ≤ z  ≤ 1.3975)

NORMSDIST(-1.3975) = .0811

P(sample mean is within 5 days of the population mean) = 1+-+2%2A.0811