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

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 = 1790 + 1.1x. (a) What is the expected value of 28-day strength when accelerated strength-2560? 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 strenth to change when accelerated strength increases by 150 psi? (d) By how much can we expect 28-day strength to change when accelerated strength decreases by 150 psi? psi

Explanation / Answer

y = 1790 + 1.1 x

a) x = 2560

y = 1790 + 1.1 * 2560 = 4606

b) We can expect 28-day strength to increase by 1.1 psi when accelerated strength increases by 1 psi

c) We can expect 28-day strength to increase by 150 * 1.1 = 165 psi when accelerated strength increases by 150 psi

d) We can expect 28-day strength to decrease by 150 * 1.1 = 165 psi when accelerated strength decreases by 150 psi

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