The deflection temperature under load for two different types of plastic pipe is being investigated. Two random samples of 15 pipe specimens are tested, and the

deflection temperatures observed are as follows (in Fahrenheit ):

Type 1: 206 188 205 191 194 193 207 185 189 213 192 210 194 198 205

Type 2: 177 197 206 200 180 176 185 200 197 192 198 188 189 203 192

(a) Construct the normal probability plots (and tests) for the two samples. Do these

plots provide support for the assumptions of normality and equal variances? Write a

practical interpretation for these plots.

(b) Do the data support the claim that the deflection temperature under load for type 1

pipe exceeds that of type 2? In reaching your conclusions, use α = 0.05.

(c) Calculate a P-value for the test in part (b).

(d) Construct a 90% confidence interval for the difference in mean deflection

temperature of the two types of pipe. Interpret this interval.

My question is: how (b) is the test of the two variances? I don't understand this point