Representative data on x = carbonation depth (in millimeters) and y = strength (in mega pascals) for a sample of concrete core specimens taken from a particular building were read from a plot in the article “The Carbonation of Concrete Structures in the Tropical Environment of Singapore” (Magazine of Concrete Research [1996]: 293-300);

Depth, x             8            20            20            30            35            40            50            55            65 

Strength, y      22.8        17.1         21.1         16.1        13.4        12.4         11.4           9.7           6.8

a) Construct a scatterplot. Does the relationship between carbonation depth and strength appear to be linear? 

b) Find the equation of the least-square line. • What would you predict for strength when carbonation depth is 25 mm? 

c) Explain why it would not be reasonable to use the least-square line to predict strength when carbonation depth is 100 mm.