A certain auto repair shop services a particular make of car in the downtown region of a particular city. Three years ago, 4% of all repairs at this shop were not successful --- the mechanics were not able to restore the car to a drivable state. This year, only 2% of all repairs were not successful. Clearly, the mechanics training course, given over a year ago, has considerably increased the skill of mechanics at this particular shop
that fewer cars are beyond their ability to repair.
A new shop uptown specializes in repairing cars of this make more than six years old, and most of these older cars are taken to this shop.