A manufacturer of concrete bridge supports is interested in determining the effect of varying the sand content of concrete on the strength of the supports.

Five supports are made for each of five different amounts of sand in the concretemix and each support tested for compression resistance. The results are as shown in Table 6.31.

Table 6.31 Data for Exercise 4 Percent Sand Compression Resistance (10,000 psi)

15 7 7 10 15 9 20 17 12 11 18 19 25 14 18 18 19 19 30 20 24 22 19 23 35 7 10 11 15

(a) Performthe analysis to determinewhether there is an effect due to changing the sand content.

(b) Use orthogonal polynomial contrasts to determine the nature of the relationship of sand content and strength. Draw a graph of the response versus sand amount. LO.1