Question

According to the National Health Statistics Reports, the standard deviation of the weights of all one-year-old baby boys born in the U.S. is 5.3 pounds. A random sample of 360 one-year-old baby boys born in the U.S. had a mean weight of 25.5 pounds.
a) Construct a 90% confidence interval for the mean weight of all one-year-old baby boys in the U.S. Write a sentence that interprets this interval.
b) Should this confidence interval be used to estimate the mean weights of all one-year-old babies in the U.S.? Explain.

Answer 1

Answer: A) At 90% confidence interval estimate of the population mean

is,( 25.0405 , 25.9595 )

B) YES

Step-by-step explanation:

Given that,

Point estimate = sample mean  Ж = 25.5

Population standard deviation α  = 5.3

Sample size = n =360

At 90% confidence level the z is ,

∝ = 1 - 90% = 1 - 0.90 = 0.1

∝ / 2 = 0.1 / 2 = 0.05  

Z∝/2 = Z0.05 = 1.645 ( WHEN WE USE THE Z TABLE )

Margin of error E = Z∝/2 * ( α/√n)

E = 1.645 * (5.3 / √360 )  = 0.4595

At 90% confidence interval estimate of the population mean

is

Ж - E < ц < Ж + E  

25.5 - 0.4595 <  ц < 25.5 + 0.4595  

25.0405 <  ц < 25.9595  

( 25.0405 , 25.9595 )

At 90% confidence interval estimate of the population mean

is,( 25.0405 , 25.9595 )

B) This confidence interval can be used to estimate the mean weight of all one - year old babies in the US since the mean value of 25.5 falls within the confidence values, we have sufficient evidence to

conclude that the mean weight of all one-year-old boys is 25.5