The Smith family has five members: Mom, Dad, Ed, Lisa, and Judy. Each family member owns a
dog. The family and their dogs were out hiking when they encountered a river they needed to
cross. They rented a boat which could hold three living things (people or dogs). Unfortunately,
the dogs were temperamental: each was comfortable only with its owner and could not be near
another person, not even momentarily, unless its owner was present. Dogs could be with other
dogs, however. The crossing would have been impossible except that Lisa's dog had attended a
first-rate obedience school and knew how to operate the boat. No other dogs were that well-
educated. How was the crossing arranged, and how many trips did it take? (Note: Lisa's dog,
though well-educated, was just as temperamental as the other dogs.)
