[Photo by mape_s.]
I’m afraid that Math Club may have fallen victim to the economy, which is worse in our town than in the nation in general. Homeschooling families have tight budgets even in the best of times, and now they seem to be cutting back all non-essentials. I assumed that last semester’s students would return, but I should have asked for an RSVP.
Still, Kitten and I had a fun time together. We played four rounds of Tens Concentration, since I had spread out cards on the tables in the library meeting room before we realized that no one was coming. Had to pick up the cards one way or another, so we figured we might as well enjoy them! She won the first two rounds, which put her in a good mood for our lesson.
I had written “Prime numbers are like monkeys!” on the whiteboard, and Kitten asked me what that meant. That was all the encouragement I needed to launch into my planned lesson, despite the frustrating dearth of students. The idea is taken from Danica McKellar’s book Math Doesn’t Suck.
Prime Numbers . . . and Monkeys
Quoting from Ms. McKellar’s book:
Some numbers of beads cannot be evenly divided up no matter what you do. Lots of small numbers are like that: 2, 3, 5, 7. The only factors they have are 1 and themselves. There are bigger numbers like that, too, like 53 and 101. It’s hard to believe that there’s no way to evenly divide up 101, but it’s true!
I like to think of these numbers as less “evolved” than most numbers. They don’t have a whole lot going on upstairs, if you know what I mean. They’re uncomplicated. They’re “primitive,” like monkeys. (Monkeys are a type of primate.) And perhaps that is why these less-evolved numbers are called prime.
Yes, prime numbers are a bit like monkeys. Just go with me on this, okay?
Kitten is a writer, so she enjoyed the wordplay.
More from Ms. McKellar:
Like monkeys swinging on the lowest branches of trees, prime numbers swing off the lowest branches of factor trees.
A factor tree is a pencil-and-paper visualization of breaking a number into its prime factors. Every number is either prime itself or it can be written as the product of two or more prime numbers.
We can show this in a factor tree, where each pair of branches show two numbers that can be multiplied to make the number above them. When we find a prime factor, we circle it.
When the tree is finished, we look for all the circled numbers. Those are the prime numbers that multiply together to make the number we started with.
After I did 24 as an example, it was Kitten’s turn. She factored 84:
We noticed that if 1 was allowed to count as a prime number, the factor tree would keep branching forever and we would never get to snack time. Definitely not a good thing! No wonder mathematicians don’t count 1 among the primes.
Then we worked together to factor 700,700. Kitten finished up the lesson by figuring out that today is January , .
With no other kids around (and Mom trying to stick to her diet), Kitten got first dibs on the snacks. We finished up the last two games of Concentration, then cleaned the meeting room and stacked all the chairs.
On the way home from the library, Kitten said, “I like Prime Monkeys. They’re fun!”
From a child who once wrote “I hate hate hate hate hate hate math!” all over the back of her Miquon workbook, that is high praise, indeed.
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