Question

a sample of 279 one year old baby boys in the US had a mean weight of 25.9 pounds. assume the population standard deviation is 5.9 pounds. what is the upper bound of the 90% confidence interval for the mean lifetime of the components. round your answer to two decimal places

Answer 1

Solution :

Given that,

Point estimate = sample mean = = 25.9

Population standard deviation =    = 5.9

Sample size = n = 279

At 90% confidence level

= 1 - 90%  

= 1 - 0.90 =0.10

Z = Z_0.10 = 1.282

Margin of error = E = Z * ( /n)

= 1.282 * ( 5.9 /  279 )

= 0.45

At 90% upper bound confidence interval estimate of the population mean is,

+ E

= 25.9 + 0.45

upper bound = 26.35