=+38. A regression analysis carried out to relate y 5 repair time for a water filtration system (hr) to x1 5 elapsed time since the previous service (months) and x2 5 type of repair (1 if electrical and 0 if mechanical) yielded the following model based on n 5 12 observations: yn 5 .950 1 .400x1 1 1.250x2. In addition, SSTo 5 12.72, SSResid 5 2.09, and sb2 5 .312.