The accompanying data resulted from an experiment to investigate whether yield from a certain chemical process depended either on the formulation of a particular input or on mixer speed.

A statistical computer package gave , and .

a. Does there appear to be interaction between the factors?

b. Does yield appear to depend on either formulation or speed?

c. Calculate estimates of the main effects.

d. The fitted values are , and the residuals are . Verify that the residuals are .23, , .63, 4.50, , , , 1.97, .07, , , 1.40, .67, , .57, , , and 3.57.

e. Construct a normal probability plot from the residuals given in part (d). Do the ’s appear to be normally distributed?