92. The following summary data on bending strength

(lb-in/in) of joints is taken from the article Bending Strength of Corner Joints Constructed with Injection Molded Splines (Forest Products J., April 1997: 89—92). Assume normal distributions.

Sample Sample Sample Type Size Mean SD Without side coating 10 80.95 9.59 With side coating 10 63.23 5.96

a. Calculate a 95% lower con dence bound for true average strength of joints with a side coating.

b. Calculate a 95% lower prediction bound for the strength of a single joint with a side coating.

c. Calculate an interval that, with 95% con dence, includes the strength values for at least 95% of the population of all joints with side coatings.

d. Calculate a 95% con dence interval for the difference between true average strengths for the two types of joints.