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 = 1800 + l.lx. What is the expected value of 28-day strength when accelerated strength = 2530?____psi By how much can we expect 28-day strength to change when accelerated strength increases by 1 psi?______psi By how much can we expect 28-day strength to change when accelerated strength increases by 50 psi?____psi By how much can we expect 28-day strength to change when accelerated strength decreases by 50 psi?______psi

Explanation / Answer

y = 28-day standard-cured strength (psi)

x = accelerated strenght (psi)

The equation of true regression line is y = 1800 + 1.1 x

(a) What is the expected value of 28-day strenght when accelerated strenght = 2530

So y = 1800 + 1.1* 2530 = 4583

(b) When accelerated strenght increase by 1 psi, 28-day strenght increase by 1.1.

(c) when accelerated strenght increase by 50, 28-day strenght increase by 50*1.1 = 55.

(d) when accelerated strenght decrease by 50, 28-day strenght decrease by 50*1.1 = 55.

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