My Notes Ask Yos 10 points DevoreSta9 12 E.007 An article\'on estimating 28-day

Question

My Notes Ask Yos 10 points DevoreSta9 12 E.007 An article'on estimating 28-day strength of concrete considered regressing y-28-day regression line is y -1850+1.3x standard-cured strength (psi) against x - accelerated strength (psi). Suppose the equation of the true (a) What is the expected value of 28-day strength when accelerated strength 2560? (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 60 pai psi (d) By how much can we expect 28-day strength to hange when accelerated strength decreases by 60 psi psi Need Help? 1.un-Lete.MI

Explanation / Answer

Answer

(A) we have regression equation y = 1850 + 1.3*x

we have to find y when x= 2560

putting x = 2560 in the regression equation, we get

y = 1850 + 1.3*2560 = 1850+3328 = 5178 psi

(B) since the slope of the regression equation is 1.3, this means for every 1 unit increase in x value, the y value will be increase/decrease by 1.3 units.

so, for 1 psi increase in x, we have 1.3 psi increase change in y

(C) since the slope of the regression equation is 1.3, this means for every 1 unit increase in x value, the y value will be increase/decrease by 1.3 units.

so, for 60 psi increase in x, we have 1.3*60 = 78 psi increase change in y

(D) since the slope of the regression equation is 1.3, this means for every 1 unit increase in x value, the y value will be increase/decrease by 1.3 units.

so, for 60 psi decrease in x, we have 1.3*(-60) = -78 psi or decrease of 78 psi change in y

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