Q$-10,$ Page $294$

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 concrete mix and each support tested for compression resistance. The results are as shown in the following table.

$\backslash$table$[[$Percent Sand,Compression Resistance $(10,000$ psi$)],[15,7,7,10,15,9],[20,17,12,11,18,19],[25,14,18,18,19,19],[30,20,24,22,19,23],[35,7,10,11,15,11]]$

a$.$ Perform the analysis to determine whether there is an effect due to changing the sand content.

b$.$ Use Tukey's HSD to make all pairwise comparisons between the percent of sand, using either a table of means or a line graph, and summarize the results in a short paragraph.