Question

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