10.149 [EX10-149] The material used in making parts affects not only how long the part lasts but also how difficult it is to repair. The following measurements are for screw torque removal for a specific screw after several operations of use. The first row lists the part number, the second row lists the screw torque removal measurements for assemblies made with material A, and the third row lists the screw torque removal measurements for assemblies made with material B. Assume torque measurements are normally distributed.

Removal Torque (NM, Newton-meters)

Part Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Material A 16 14 13 17 18 15 17 16 14 16 15 17 14 16 15 Material B 11 14 13 13 10 15 14 12 11 14 13 12 11 13 12 Source: Problem data provided by AC Rochester Division, General Motors, Rochester, NY

a. Find the sample mean, variance, and standard deviation for the material A data.

b. Find the sample mean, variance, and standard deviation for the material B data.

c. At the 0.01 level, do these data show a significant difference in the mean torque required to remove the screws from the two different materials?