11.79 A company that services two brands of microcomputers would like to be able to predict the amount of time it takes a service person to perform preventive maintenance on each brand.

It believes the following predictive model is appropriate:

Y = b0 + b1x1 + b2x2 + e SSE R2 First-order 8.548 0.950 Second-order 6.133 0.964 R2 e

a = 0.05 Ha: b2 Z 0 H0: b2 = 0 a = 0.05 where maintenance time service person’s number of months of experinece in preventive maintenance Ten different service people were randomly selected, and each was randomly assigned to perform preventive maintenance on either a brand A or brand I microcomputer. The data in table below were obtained.
a Fit the model to the data.
b Investigate whether the overall model is useful.
Test using .
c Find for the fitted model. Does the value of support your findings in part (b)?
Explain.
d Find a 90% confidence interval for . Interpret your result in the context of this exercise.
e Use the fitted model to predict how long it will take a person with six months of experience to service a brand I microcomputer.
f How long would it take the person referred to in part

(e) to service 10 brand I microcomputers?
List any assumptions you made in reaching your prediction.
g Find a 95% prediction interval for the time required to perform preventive maintenance on a brand A microcomputer by a person with four months of experience.