An article on estimating 28-day strength of concrete considered regressing y = 2

Question

An article on estimating 28-day strength of concrete considered regressing y = 28-day standard-cured strength (psi) against x = accelerated strength (psi). Suppose the equation of the true regression line is y = 1760 + 1.5x. (a) What is the expected value of 28-day strength when accelerated strength = 2440? psi (b) By how much can we expect 28-day strength to change when accelerated strength increases by 1 psi? psi (c) By how much can we expect 28-day strength to change when accelerated strength increases by 100 psi? psi (d) By how much can we expect 28-day strength to change when accelerated strength decreases by 100 psi? psi

Explanation / Answer

a) y = 1760 + 1.5 X 2440 = 1760 + 3660 = 5420

b) 28 day strength change by 1.5 units for 1 unit change in accelerated strength

c) 150

d) 150 decrease

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