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This is a great little Chinese folktale by Lily Toy Hong. It's the story of Mr. Haktak and his wife. They are very old and very poor. One day Mr. Haktak returns from the garden with a brass pot he has dug up. Soon, the couple discover that anything they place in the pot duplicates itself exactly! So, if you put in a purse with ten gold coins, then you pull out two purses, each with ten gold coins. Of course, the couple gets busy duplicating coins! Also, of course, they have an accident and Mrs. Haktak falls into the pot-- making two Mrs. Haktaks! You will have to read the book to find out how they solve the dilemma of having too many wives!
Here's how I use it in the classroom. After reading the book I talk to the class about things we need in the room-- like a laptop computer for everyone. Then I pose the problem: If I put my laptop in the pot, how many times would we have to keep putting in laptops to get exactly the number we need- no extras? I also add to the problem this requirement: What would be the smallest number of duplications that would solve the problem--obviously we can just keep putting in one at a time. I divide the students into groups and give each group a large piece of paper and let them go about solving the problem. It's actually trickier than it seems.
Once we have solved this one I give them a new problem- maybe starting with a different beginning amount. They always love this book and the problems. It really makes them think! (It also helps that little kids love magic!)