1. A paint manufacturer is developing a new type of paint. Thirty panels were exposed to various
corrosive conditions to measure the protective ability of the paint. The mean life for the samples
was 168 hours, with a sample standard deviation of 22 hours.
a. (5 points) Use this information to compute a 90% confidence interval for the population
mean life of the new paint. Also show that you checked to make sure the data meet all
necessary conditions for inference.
Conditions for Inference:
•
•
Name of calculator test used:
Confidence interval values: ( , )
b. (5 points) Fill in the blanks in the statement below to write a correct interpretation of the
interval you found in part a.
We are ________% confident that the population _________________________________
is between ________________ and ___________________.
2. A local cable company thinks that many of their customers may have more outlets wired than
they are paying for. A random sample of 400 houses reveals that 110 have excessive outlets.
a. (5 points) Use this information to compute a 99% confidence interval for the population
proportion of homes with more outlets than they are paying for. Also show that you
checked to make sure the data meet all necessary conditions for inference.
Conditions for Inference:
•
•
Name of calculator test used:
Confidence interval values: ( , )
b. (5 points) Fill in the blanks in the statement below to write a correct interpretation of the
interval you found in part a.
We are ________% confident that the population _________________________________
is between ________________ and ___________________.