Fairy Tale Math Circle #6

There was no fairy tale for this meeting, not as such. Instead, we just talked about all the different fairy tale creatures – Baba Yaga, Kashey the Immortal (not a good guy, overly obsessed with gold), Ivan the Fool, the three-headed dragon, etc.


We started with figuring out how to “magically” turn five ones into different numbers using only + and – signs. Most everyone figured out how to get 1, 3 and, of course, 5. But how do you get 100?! The kids worked on this for a while until, one by one, they figured it out. Once they got the idea, they were quick with the remaining numbers.

I was a bit worried about V (the youngest) and M (he really dislikes arithmetic). Both worked so hard on these! Surprisingly, after the meeting, M said that this was the problem he liked the most because “it wasn’t obvious what to do and I had to think hard about it.”


We switched to a logic problem next.

The cat always sneezes 24 hours before it rains. Today the cat sneezed and I said: “It will rain tomorrow.” Am I right?

Initially only D thought that I was wrong. But, after seeing that everyone else thought my statement was true, he changed his mind and joined the majority. Well, they were surprised to hear that the statement was false. It took a while to figure out why. After several attempts to establish the exact timing of the cat’s sneeze (how about 00:00?), Nk figured out the solution and explained it to others.


At this point A and N joined us (back from their summer break), just in time for the problem about finding a fake gold coin in a pile of 9 coins. The fake one weighs less. What’s the smallest number of weight-ins necessary to find the fake coin? Does luck have anything to do with the solution? A quickly figured out the answer, but the rest kept working on it for some time using paper plates and plastic fusing beads to model the process (paper plates and plastic beads RULE! It seems like we use them every single week).


It was definitely time to change the pace. Here we were doing some jumping around and screaming the answers to the next problem (about ships sailing between two islands). I stated the problem and, as usual, got swamped with the answers (time to be more forceful about the mandatory thinking period). “Two, three, none”, the kids shouted. So I suggested that maybe if we scream our favorite answer loud enough, then it would be the correct one. It always works – after a minute or two everyone is smiling and ready to get back to thinking.


I actually went ahead and gave them the correct answer to the problem.Their challenge was to figure out the way to arrive at the answer. We did some role-playing and then, all of a sudden, N had this big breakthrough. And she was able to explain the key idea that got overlooked by everyone else. This was really exciting!


And then it was time for the experiment. In keeping with the “fake gold coins” problem, I selected the electroplating experiment. We attempted to electroplate a penny with zinc.


It worked beautifully! Even better than when I tried it on my own at home. Everyone got to take some part in the experiment – connecting alligator clips, inserting batteries into the battery holder, lowering and securing the anode and cathode.


I think, this was the most successful experiment to date because the kids didn’t just do it, but actually discussed ideas about the what’s and the why’s of the process.

To be continued next week…


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