## The Activities

**Topic: Subtraction:**Book: Shark Swimathon by S. Murphy.**Topic: Sorting:**The kids sorted numbered cards from 1 to 104, trying for a new world record.**Topics: Charts, Graphs:**We simulated a race between a tortoise and a hare, where the hare tortoise started in Box 8 and moved 1 square a turn and the hare started in Box 0 and moved 2 squares a turn. First we each made a table of the positions of the tortoise and hare at each step (in two columns), and figured out when the hare would pass the tortoise. Then we plotted these positions with time as the X axis and position of the Y axis, using different symbols (X vs. O) for the tortoise vs. hare. Then, we added two more even faster animals, which started at 0 after some number of steps.

**Topic: Programming:**We did a new kind of programming based on the iOS game CargoBot (which I highly recommend). In this game, you control a claw arm which can move Left, Right, or Down; when it moves Down, it grabs a block if it doesn’t currently have one, and drops its block if it doesn’t. The goal is to move the blocks from a given starting position to a different given ending position. This week, the first problem was to flip a tower over onto the adjacent space (note that there can be several colors of blocks). The second problem was to move a tower two boxes over, WITHOUT flipping it.

## How Did It Go?

We had all five kids this week.

#### Shark Swimathon

Pretty straight-forward math (simple two-digit subtraction), but the kids liked the story about the sharks.

#### Sorting

This was the first time in a while we had all five kids for the card sorting activity. They’ve now got the radix sort strategy down pretty well (i.e., putting cards directly where they should go). There was still some unnecessary work (moving cards around to make space, even though it was ok if the cards overlapped) and not everyone contributed the whole time. But the kids beat the previous record by a substantial margin, successfully sorting all 104 cards in 5:40.

#### Graphing the Race

I had a race track with numbers 0-40 and a couple of markers for the animals. We simulated the race until the hare caught the tortoise. The kids are pretty good at tables now and had no problems recording the positions. They also noticed the pattern and started adding to their tables without using the simulation. The graphing was tricky for them, as it has been in the past, but I think it went better than it has before. For one thing, they again noticed the pattern, so they didn’t have to count from scratch for each new point. They did often make mistakes like going right 1 and up 3 instead of right 1 and up 4 (for the ostrich). In retrospect, I should have make the Y axis be time, going down, and the X axis be position. Then each row would correspond to a snapshot of the race. I did explain that each column was a snapshot of the race, I’m not sure if they understood. This was the first time we’ve gotten nice graphs of straight lines, and the kids were pretty into it and probably would have kept going for a while with new animals.

#### Cargo Bot

The kids picked this up faster than I expected. One kid immediately started using L, R, and D as short-hand, which we’ll explicitly suggest in the future since it saves a lot of time. About half the kids solved or nearly solved the first problem on their first try, getting the pattern of RDLD. For the others, I simulated using my hand their instructions and they saw the bugs in their programs. One of the kids solved the first problem quite a bit faster than the others and started work on the second; they got a solution that moved the tower over 2 spaces but inverted the order of the blocks.

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