17. 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.

Carbon Sand Fiber Addition Addition Casting Wet-Mold

(%) (%) Hardness Strength 0 0 61.0 34.0 0 0 63.0 16.0 15 0 67.0 36.0 15 0 69.0 19.0 30 0 65.0 28.0 30 0 74.0 17.0 0 .25 69.0 49.0 0 .25 69.0 48.0 15 .25 69.0 43.0 15 .25 74.0 29.0 30 .25 74.0 31.0 30 .25 72.0 24.0 0 .50 67.0 55.0 0 .50 69.0 60.0 15 .50 69.0 45.0 15 .50 74.0 43.0 30 .50 74.0 22.0 30 .50 74.0 48.0

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

b. Carry out an ANOVA on the casting hardness observations using 
.05.

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