10.48 [EX10-048] “Is the length of a steel bar affected by the heat treatment technique used?” This was the question being tested when the following data were collected.

Heat Treatment Lengths (to the nearest inch)

1 156 159 151 153 157 159 155 155 151 152 158 154 156 156 157 155 156 159 153 157 157 159 158 155 159 152 150 154 156 156 157 160 2 154 156 150 151 156 155 153 154 149 150 150 151 154 155 155 154 154 156 150 151 156 154 153 154 149 150 150 151 154 148 155 158

a. Find the means and standard deviations for the two sets of data.

b. Find evidence about the sample data (both graphic and numeric) that supports the assumption of normality for the two sampled populations.

c. Find the 95% confidence interval for 1  2.