As concrete cures, it gains strength. The following data represent the 7-day and 28-day strength (in pounds per square inch) of a certain type of concrete.

(a) A scatter diagram of the data is shown next. What type of relation appears to exist between 7-day strength and 28-day strength?

(b) The residual plot on the next page was obtained after finding the least-squares regression line. Does the residual plot confirm that the relation between 7-day and 28-day strength is linear?

(c) The coefficient of determination is 57.5%. Provide an interpretation of this value.

Transcribed Image Text:

7-Day Strength, x 28-Day Strength, y 7-Day Strength, x 28-Day Strength, y 2480 4120 2300 4070 5220 3380 3390 5020 2430 4640 2660 4890 2890 4620 2620 4190 3330 4850 3340 4630 28-Day vs. 7-Day Concrete Strength 5200 5000 4800 - 4600 8 4400 4200 - 2400 2600 2800 3000 3200 3400 7 Day (Ib/in³) 28 Day (Ib/in)