The quality control director for a clothing manufacturer wants to study the effect of machines on the breaking strength (in pounds) of wool serge material. A batch of the material is cut into square-yard pieces, and these are randomly assigned, 12 each, to the three machines chosen specifically for the experiment. The results (stored in the file Breakstw) are shown at the top of the next column: At the 0.05 level of significance,

a.) Is there an effect due to machine?
b.) Plot the mean breaking strength for each machine.
c.) If appropriate, use the Tukey-Kramer procedure to examine differences among machines.
d.) What can you conclude about the effects of machines on breaking strength? describe.
File (Breakstw):

I II III
115 111 109
115 108 110
119 114 107
117 105 110
114 102 113
114 106 114
109 100 103
110 103 102
106 101 105
112 105 108
115 107 111
111 107 110