A typing instructor builds a regression model to investigate what factors determ

Question

A typing instructor builds a regression model to investigate what factors determine typing speed for students with two months of instruction. Her regression equation looks likes: Y’=7X2+5X2+3X+11 Where Y’= typing speed in words per minute; X3= hours of instruction per week; X2= hours of practice per week; X= hours of typing per week necessary for school or work; A new student is taking 2 hours of typing instruction per week, will practice 5 hours per week and must type 2.5 hours per week for work. If the standard error of the estimate is 4, within what range do we have a 94.45% probability that that students typing speed will be in two months. (I did the work and I think its D, i got 45.50 then added the standard error of 4 to each side... i am not sure about the probability aspect and how it plays into the question)

A. 53.5 and 61.5 WPM

B. 49.5 and 65.5 WPM

C. 57.5 and 65.5 WPM

D. none of the above

Explanation / Answer

Note that 95.45% probability means 2 standard errors around the best estimate.

As

Y’=7X3+5X2+3X+11

Then

Y’=7*2+5*5+3*2.5+11 = 57.5

Hence, adding/subtracting 2 standard errors (2*4 = 8), then

57.5 - 8 = 49.5
57.5 + 8 = 65.5 [ANSWER, B]

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