Age 6

## The Activities

**Topics: Numbers, Codes, Algebra:**The Cat in Numberland, Chapter 3, by I. Ekeland. In this chapter the letters come to visit the numbers, and we learn about letter/number ciphers and letters standing in for numbers.**Topic: Algebra:**I made problems of the form “X + 3 = 5” using unit cubes from Base Ten Blocks and a small cardboard box. I.e., I would secretly put 2 blocks into the box and close it, put 3 blocks next to it, and then say “There are 5 blocks total, how many are in the box?”**Topic: Primes:**I introduced the idea of primes using Base Ten Blocks: a number N is a prime if the only rectangle you can make using N blocks is 1 X N. I gave different numbers to each kid and had them figure out whether it was prime or not.**Topics: Combinations, Combinatorics:**I printed a bunch of “Easter eggs” with a top and bottom section. Using five different colors of crayons, I asked the kids to make as many different eggs as they could, coloring each section in solid colors (not stripes/dots/etc.). I taped each one to the wall (stacking repeats).

## How Did It Go?

We had four kids this week.

#### Cat In Numberland

The algebra in this chapter is tricky because it includes addition, subtraction, multiplication, and division; most of the kids don’t know multiplication or division yet.

#### Box Algebra

This worked pretty well. The kids understood what was going on right away, and they were always excited when I opened the box and dumped out the blocks inside to see if their guess was correct. At the end they made a problem for me, which was something like “X + 3 = 39” (of course, they used as many blocks as they could).

#### Rectangle Primes

We did up to about 14. I kept track of each result. The only odd composite number <= 14 is 9, so for the most part they just needed to check a 2 row rectangle. Proving something is prime is tricky, of course, and whenever a kid said that something was prime, I always asked them “did you check 3-wide”? Whoever had 9 didn’t initially check 3×3.

#### Easter Eggs

The kids were really into this activity and worked very hard to get all the combinations. They got all 10 two-color combinations pretty quickly and without help (first two rows in picture above) — but there was no pattern to which color was on top vs. bottom. Then one of the kids realized that you could flip the colors. They quickly got 6 more, but the next 3 took them a lot longer to find, and I had to help them find the last one. This got them to 20, but they didn’t think of having the same color on top and bottom. I suggested it to them and they quickly made the last 5. Then I rearranged them so that there were same color tops along the rows and same color bottoms along the columns. I realized afterwards that I should have made this chart before I gave them the hint about same color top/bottom, because then there would have been gaps and I could ask them what went in the gaps.