Question 495636: A family of 5 and their 5 dogs were hiking when they encountered a river to cross. They rented a boat which could only hold 3 living things. Unfortunately, the dogs were only comfortable with its owner and couldn't be near another person unless its owner was present. Dogs could be with other dogs however. The crossing would have been impossible, but Lisa's dog had attended a first-rate obedience school and knew how to operate the boat. No other dogs were that educated. How was the crossing arranged and how many trips did it take?
Answer by Theo(13342)   (Show Source):
You can put this solution on YOUR website! first trip:
lisa goes over with 2 people
lisa comes back.
there are 2 people on the other side
second trip:
lisa goes over with 2 people
lisa comes back.
there are 4 people on the other side
third trip:
lisa's dog goes over with 2 dogs
lisa's dog comes back
there are 4 people and 2 dogs on the other side
fourth trip:
lisa's dog goes over with 2 dogs
lisa's dog comes back
there are 4 people and 4 dogs on the other side
fifth trip:
lisa goes over with her dog
nobody comes back
there are 5 people and 5 dogs on the other side
it took 5 trips total.
if the dog was not able to drive the boat, then it would have required the following:
first trip:
lisa goes over with 1 person and their dog.
lisa comes back
1 person and 1 dog is on the other side
second trip:
lisa goes over with 1 person and their dog.
lisa comes back
2 people and 2 dogs are on the other side
third trip:
lisa goes over with 1 person and their dog
lisa comes back
3 people and 3 dogs are on the other side
fourth trip:
lisa goes over with 1 person and their dog
lisa comes back
4 peopleand 4 dogs are on the other side
lisa goes over with her dog
nobody comes back
5 people and 5 dogs are on the other side
it would have taken 5 trips either way.
the crossing was not impossible.
it did not require the dog to know how to operate the boat.
not as far as i can tell.
every trip did not require lisa to operate the boat.
anybody could have done it.
there was no restriction on what person could operate the boat.
5 trips were required either way.
on the last trip, there was no return.
if you count each way as a trip, then 9 trips were required.
5 going and 4 coming back.
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