The article “Towards Improving the Properties of Plaster Moulds and Castings” (J. Engr. Manuf., 1991: 265–269)

describes several ANOVAs carried out to study how the amount of carbon fiber and sand additions affect various characteristics of the molding process. Here we give data on casting hardness and on wet-mold strength.

a. An ANOVA for wet-mold strength gives , and . Test for the presence of any effects using . a 5 .05 SSFiber 5 1278, SSE 5 843 SST 5 3105 SS Sand 5 705,

b. Carry out an ANOVA on the casting hardness observations using .

c. Plot sample mean hardness against sand percentage for different levels of carbon fiber. Is the plot consistent with your analysis in part (b)?