An experiment was performed to compare abrasive wear of 2 different laminated materials. Twelve pieces of material 1 were tested by exposing each and every piece to a machine measuring wear. Ten pieces of material two were similarly tested. In each case, the depth of wear was observed. The samples of material one gave an average (coded) wear of 85 units with sample standard deviation of 4, while the samples of material 2 gave average of 81 and sample standard deviation of 5. Suppose the populations to be approximately normal with equal variances.
a) Can we conclude at the 0.05 level of significance that abrasive wear of material 1 exceeds that of material 2 by more than 2 units?
b) Repeat part (a) if n1=n2=60.