The article “Some Field Experience in the Use of an Accelerated Method in Estimating 28-Day Strength of Concrete” (J. of Amer. Concrete Institute, 1969: 895) consid ered regressing standard-cured strength (psi)
against . Suppose the equation of the true regression line is .

a. What is the expected value of 28-day strength when accelerated strength ?

b. By how much can we expect 28-day strength to change when accelerated strength increases by 1 psi?

c. Answer part

(b) for an increase of 100 psi.

d. Answer part

(b) for a decrease of 100 psi.