Answer
Concrete for which slump is 3.5 inches and 7-day strength is 2450 psi:
The 95% confidence interval is between 3988.57 and 4427.24 psi.
The 95% prediction interval is between 3533.62 and 4882.20 psi.
Work Step by Step
In MINITAB, enter the Slump values in C1, the 7-Day psi values in C2 and the 28-Day psi values in C3.
Select Stats -> Regression -> Regression -> Predict
Enter 3.5 and 2450 in the first row of the table.
Click in Options and enter the level of confidence. Click OK.
Click OK.
