# Number Talk Part 3

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## number talk part 3

5th - 6th Grade Math - Guess My Rule
Fran Dickinson, San Carlos Charter Learning Center, San Carlos School District, San Carlos, California

Previous:  Number Talk Part 2

FRAN DICKINSON: All right. Ryan, it looks like you have a question.

STUDENT: Um, well I have, I have a question for Teo. If it was a x val, y value, wouldn’t you do the opposite of the x? So wouldn’t you divide, maybe?

STUDENT: I don’t know. Do you know, Griffin?

FRAN DICKINSON: Griffin, you want to respond to that?

STUDENT: yeah. Well, I did it backwards, and I said, plus 3 instead of minus 3, and then divided by 3. So 0 plus 3 is 3, divided by 3 is 1.

FRAN DICKINSON: So we’re doing a lot of talking about this rule. What is the rule? Can we write a rule here? That might help us to understand what Griffin was saying by working backwards. Maggie?

STUDENT: x, 3, minus 3. No. x 3 minus 3.

FRAN DICKINSON: x3-3. Can you just kind of walk us through, what this is here?

STUDENT: like, x3 is x times 3.

FRAN DICKINSON: Okay. So x3 means x times 3? And then take away 3. So, I see some silent disagreement around the room. Is there anyone who cares to make a comment about that? Sam. Adams.

STUDENT: Well, maybe you could change that, I agree with x3-3 equals y, but maybe you can add something to it? x3-3=y?

FRAN DICKINSON: Oh, okay. So you would just like to add “equals y.”

STUDENT: if some people could be unclear.

FRAN DICKINSON: My apologies for running out of space on my card here, but I’ve written “=y.” I think that’s a nice suggestion. I see some more silent disagreement in the room. Yes. Jonah?

STUDENT: I think it would make more sense if it said times 3 minus 3. Not x3 minus 3 because….

FRAN DICKINSON: So what do you propose, though?

STUDENT: Instead of, like saying x3, that could sound like, it’s like a number instead of 3. It should just be times 3 minus 3.

FRAN DICKINSON: On our chart. So you’re saying times 3, uh, minus 3.

STUDENT: Yeah.

FRAN DICKINSON: That’s how you want to define that rule?

STUDENT: Or put the dot there, or something…

FRAN DICKINSON: Morgan. So x • 3 – 3. All right.

STUDENT: I think that number’s mixed around. I think it’s 3x minus 3.

FRAN DICKINSON: Okay. So I can write it 3x-3. Why is this more right than this? Or is it more right than that? Do Maddie and Teo disagree? Turn to your partner and have that conversation.

STUDENT: I think this could be x groups of 3, or 3 groups of x.

STUDENT: it’s like 4 groups of 2, or 2 groups of 4. It’s the same thing, but …

STUDENT: It really matters how you look at it.

STUDENT: It matters in places, like if you have to get like, groups. Like if you have to get, like if you get 4 groups of 2, it’s different than getting 2 groups of 4.

STUDENT: Oh! I get it.

FRAN DICKINSON: Great. I heard some great conversations happening around the room. Would anyone care to repeat out what they heard at their tables? Caitlin.

STUDENT: well, we thought that like the x should go after the 3, because that was in CPM.

FRAN DICKINSON: Oh. So the book told you to do it.

STUDENT: Yeah.

FRAN DICKINSON: So it must be right.

STUDENT: The book made me do it.