Question

A sample of 215 one year old baby boys in the United States had a mean weight of 23.6 pounds. Assume the population standard deviation is 5.6 pounds. What is the upper bound of the 90% confidence interval for the mean lifetime of the components?

Round to two decimal places.

Answer 1

Solution :

Given that,

Point estimate = sample mean = = 23.6

Population standard deviation =    = 5.6

Sample size = n =215

At 90% confidence level

= 1 - 90%  

= 0.10

= 0.10

Z/2 = Z0.10 ₌ 1.28

Margin of error = E = Z/2 * ( /n)

= 1.28 * (5.6 /  215 )

= 0.49
At 90% confidence interval estimate of the population mean
is,

+ E

23.6 +0.49

23.11

upper bound = 23.11