River crossing puzzle facts for kids

A river crossing puzzle is a fun type of brain teaser. Your goal is to move things or people from one side of a river to the other. You usually want to do this in the fewest trips possible. These puzzles become tricky because of rules. For example, you might only be able to carry a certain number of items. Or, some items might not be able to be left alone together.

These puzzles have been around for a very long time! The first known ones appeared in a book called Propositiones ad Acuendos Juvenes. This book was written around the 800s. It is thought that a smart person named Alcuin wrote it. This old book included three famous river crossing puzzles. Two of them are the fox, goose, and bag of beans puzzle and the jealous husbands problem.

Famous River Crossing Puzzles

There are many well-known river crossing puzzles. Each one has its own special rules to make it a challenge.

The Fox, Goose, and Bag of Beans Puzzle

This is one of the most famous river puzzles! Imagine a farmer who needs to move a fox, a goose, and a bag of beans across a river. The farmer has a small boat. This boat can only carry the farmer and one other item at a time.

Here are the tricky rules:

• The fox cannot be left alone with the goose. The fox might eat the goose!
• The goose cannot be left alone with the bag of beans. The goose might eat the beans!

The farmer must find a way to get everything safely to the other side. Similar puzzles use a wolf, a goat, and a cabbage, or a fox, a chicken, and a bag of grain.

The Jealous Husbands Puzzle

In this puzzle, you have three married couples. They all need to cross a river. They have a boat that can only hold two people at most.

The main rule is:

• No woman can be with another man unless her own husband is also there. This means a wife can't be left alone with another man on either river bank or in the boat.

This puzzle is a bit like the missionaries and cannibals problem. In that puzzle, three missionaries and three cannibals need to cross a river. The rule there is that cannibals cannot outnumber missionaries on any bank.

The Bridge and Torch Problem

The bridge and torch problem is another classic. In this puzzle, several people need to cross a bridge at night. They only have one torch. The bridge can only hold a certain number of people at once. Each person walks at a different speed. The group must cross together, moving at the speed of the slowest person in the group. The goal is to get everyone across in the shortest time possible.

The Man, Woman, and Children Puzzle

This puzzle also comes from the old Propositiones ad Acuendos Juvenes book. In this problem, a man and a woman want to cross a river. They weigh the same. They also have two children with them. Each child weighs half as much as an adult.

The boat they have can only carry the weight of one adult. The challenge is to figure out how everyone can cross the river safely using this small boat.

Images for kids

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  Dog, sheep, and cabbage