Sunday, September 7, 2014

Math Club: River Crossing Animal Puzzles

There is a category of logic puzzles called "river crossing" puzzles. Sometimes they involve "missionaries and cannibals" or "foxes and hens" or "jealous husbands."

I took a few and adapted them for stuffed animals.

My stuffed animals were delighted to participate, of course. They love outings! Getting that many passports processed was a nightmare, but the silly beasts brought that problem upon themselves when they declared independence in "the velveteen revolution" five years ago.


Gail: An omnivore bear goes to a special market at a Renaissance Faire, where he purchases a carnivorous predator animal, an herbivorous prey animal, and a sack of magic beans. To transport them all back home, he needs to cross a river, but he has a very small boat which can only fit one item in addition to himself. Only the bear can pilot the boat. Also, the carnivore cannot be left alone with the herbivore, because--
Kids: He would eat it!
Gail: Yup. He'd stand trial for the murder later, of course, but that would be too late for the poor victim. Also, the herbivore can't be left alone with the beans for the same reason.
Kids: It's not murder if it's a plant!
Gail: Right. ANYWAY. What's the most efficient way for the farmer bear to get all his purchases across the river without anything or anybody getting eaten?
[The kids form small groups along the river and divvy up the animals.]
Kid1: I want the dragon! She's a predator!
Kid 2: Awwww. What's the zebra's name? She's an herbivore, right?
Bear: You know, I could swim across. And I think I'll try eating just one of the magic beans...
[Note: Bear ALWAYS disrupts math time. --ed.]
Gail: Now, be gentle! If you pick someone up by the ear and toss him around, you'll probably lose a finger or two. It's happened to kids at church. Bitten clean off. And don't blame me. I'm just sayin'.
Kids: [Giggle]


Here are some pictures from that day, in early December of 2013:





The kids loved the activity. The animals loved it too, but I'm afraid they kept getting distracted. After entirely too much roughhousing with each other, I told them sternly that if they couldn't behave, they wouldn't be invited back. That settled them down...mostly.

It took some kids longer than others, but eventually everyone worked out a good solution. The "boats" were just sheets of paper, but it helped the kids to model the problem tangibly and visually. ("What if we send the bear and the beans over...no, come back! The tiger is eating the unicorn! Well, what if we put the bear and the unicorn in the boat...?")

Okay, fine. There were also distracting gruesome chomping noises and dying screams and an argument about the unicorn fighting back with her horn in there, too. So they didn't always stay on task. That's part of the fun! ("Nomnomnom!!! Aaaaaargh!!!" [Scuffle] [Death rattle])

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Once that was over, we worked on another one all together:

"Three carnivorous, predator animals, and three herbivorous "prey" animals all need to cross a river. They have a boat which can fit at most two animals at a time. At no point, on either shore or in the boat, can the carnivores outnumber the herbivores, because then somebody would get eaten. The boat cannot cross the river un'manned'. What is the most efficient way to get everyone across the river without anybody getting eaten?"

I sat back and let the kids do all the work. Well, I refereed a little like "Let Gertrude tell her idea", but I let them do all the thinking. They got that one, too!

Obviously, this coming school year, I will need to try something more...tricksy.

I wonder if I could adapt the Konigsberg bridge problem for stuffed animals....?

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