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 with a sample standard deviation of 5. how many degree of freedom