After Tuesday’s talk, I wanted to continue having the students look for patterns within sets of numbers. They found it really easy to find any future term in our last talk because our starting term was the change value. For example, they knew the 10th term when counting by 3’s and starting at 3 was as easy as multiplying 3 x 10. I was curious how they would think about predicting future terms if the series did not start with the same number they were by which they were counting. I brainstormed a few possible strings students could begin to think about this and, if time went well, they could look for connections between:
I decided on the following three series:
12, 18, 24, 30….
12, 15, 18, 21…
6, 11, 16, 21….
In each one I was going to have them figure the 10th term and discuss ways they were thinking about it. The idea that I wanted to emerge is the importance of accounting for the number at which they were starting and I also wanted to see how they made their predictions. I was going to end the talk by asking what the graphing story would look like if the first term was a starting height and it continued growing at this rate to connect back to our graphing stories from the previous day. As it sometimes happens, I did not make it as far as I had hoped because some amazing conversations were happening in the very first set of numbers.
I had a student count by 6’s while I recorded, starting at 12 and stopped him after I wrote 30 on the board. I purposefully stopped there because I was curious to see if students would think about the next (5th term) and double to find the 10th as they did the day before. There was an overwhelming agreement for 72 for that exact reason, but since I got a few different answers for the 10th term, I wrote them all on the board and the proving, agreeing and disagreeing began. There was one, lone 66.
There were two proofs for 72:
– Found the 5th term as 36 and doubled it to get the tenth term.
– Did 6 x 10 to get tenth term but then added 12 because he started at 12. I was excited to see he was acknowledging where the series started and the idea of the start being important.
The lone 66, then did a simple continuous count to the 10th term proving that it would be 66. Heads tilted and eyes squinted. I realized at that moment how much I appreciated that the students looked for ways to think about the 10th term without having to count up to it, but also realized that we needed to do a little more work in thinking about what was happening in the sequence.
Since I knew I was not making it past this series of numbers, I decided to connect this set of numbers to a set in which the start was 6. I wrote them on top of each other:
12, 18, 24, 30……
6, 12, 18, 24…..
It then became clear to most that the first set’s 10th term had to be 6 ahead of the bottom one because of the start. The idea of term number and the increase from term to term started to emerge. One student said the bottom series “started one term earlier so it has to end 6 earlier than the top one.” Another student bounced off of that with “A term is 6, right?”
The debate continued and great ideas were coming out about what being the 1st term meant and then one student (the 66) said well it has to be right because (the term number +1) x 6 works for every one of them. That threw most kids for a loop and definitely not a place that I thought most of the class would be ready to engage in conversation around. I let a few students question what he meant, and I let him answer them. The biggest disconnect for students was how the term number factors into finding the number in future terms. To them the term number was just labeling and not really relevant in the values.
It was time to move into our lesson for the day and I was happy with the ideas that were emerging so I had them go back to their journals and do a quick 3 minute writing of either: what they noticed between the two, what someone else said that cleared up something for them, or something they were confused about still. It was interesting to see the word “group” popping up when that really didn’t come up in the talk…and of course there is always one that I want to find more about because it seems nothing like what the others thought about..
After this talk, we went into some pattern building with rectangular arrays and finding the nth term. So much to write about that too, but will have to save that work for another night!
Tomorrow, I want to go back to second number talk set I had intended to do today and see how the conversation builds on our thoughts from today. Do they think about the starting number now? Do they talk about the numbers as “terms”? I think I will have them journal about what they find is most important when predicting what future terms would be in the series.
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