Question

Noise levels at 7 manufacturing plants were measured in decibels yielding the following data:

138,123,142,119,130,159,139

Construct the 80% confidence interval for the mean noise level at such locations. Assume the population is approximately normal.

Step 3 of 4 :  

Find the critical value that should be used in constructing the confidence interval. Round your answer to three decimal places.

Answer 1

sample mean         x=	135.714
sample size             n=	7.00
sample std deviation s=	13.363
std error sx=s/√n=	5.0508

for 80% CI; and 6 df, critical t=		1.4400
margin of error E=t*std error                            =		7.273
lower bound=sample mean-E =		128.441
Upper bound=sample mean+E=		142.987

from above:

Step 3 of 4 :   critical value that should be used in constructing the confidence interval t=1.440