An old chestnut
goes like this:
Five people and their dogs (one dog owned by each person) want to cross a river. They only have a small boat that will hold any three of them (people and/or dogs) at a time.
However, all the dogs are temperamental, and cannot be left around other people without their owner(s) being present (in the boat or on either side of the river). Dogs can be left alone with other dogs, though.
Also, any one of the people can row the boat, but of course dogs normally cannot row. However, Lisa's dog is very intelligent, and it can row the boat.
How can they cross the river without upsetting any of the dogs?