Making eight

I am writing a book. In the process of doing this, I come across homework assignments that parents find frustrating, and that they share on social media. These almost always get me thinking, and they frequently lead to math talks with my children.

This past weekend was one such instance.

Worksheet: "The whole is 8. One part is 8. What is the other part?"

Talking Math with Your Kids is not a place to hash out the details of whether this is a well written question, or whether this was an appropriate homework assignment for this child. We can discuss that on Twitter if you like, or through my About/Contact page.

Talking Math with Your Kids is about taking opportunities to have math conversations with our children. In that spirit, I share the conversation we had in our house.

Out of the blue, I asked Tabitha (7 years old) if I could ask her a math question. It was maybe Saturday afternoon. We had nothing special going on.

Me: Tabitha, can I ask you a math question?

Tabitha (7 years old): Yes.

Me: If I have eight things, and seven of them are in one hand, how many are in the other?

T: That’s not even a math question! That’s too easy!

Me: OK. But will you answer it anyway?

T: One.

Me: OK. What if I had five in one hand?

T: And you still had 8?

Me: Yeah.

She spent a few moments thinking.

T: Three.

I had a couple other questions, which I asked and she answered. The next day, I realized that I didn’t know how she knew that second one.

She was getting ready to brush her teeth on Sunday evening when I asked whether she remembered the previous day’s conversation. She did.

Me: How did you know it was three?

T: I counted.

Me: Like this? Five, then six, seven, eight?

T: Yeah. And that’s three. But actually, I kind of already had it memorized.

Me: Oh yeah? How did you memorize it?

T: Huh?

Me: Did you try to memorize it? When I want to memorize a phone number because someone told it to me and I don’t have a pen handy, I say it over and over to myself. Did you do that with 5 + 3?

T: No! I just have counted it out a lot of times.

Now, I should also mention that I asked Tabitha, If I had 8 things, and 8 of them were in one hand, how many would be in the other? She replied Zero without much hesitation. This If I have this many in one hand, how many are in the other formulation is probably less clumsy than the If this is one part, what is the other part? formulation on the original worksheet. But the intention is the same.

So What Do We Learn?

The kind of problem Tabitha and I were working with is called Part-Part-Whole. For young children, this is different from the standard “takeaway” problem because there is no “taking away”. I didn’t eat, lose, destroy or give away any of my eight things in these problems—I just have some in one hand and some in the other.

Because Part-Part-Whole involves a different way of thinking, it’s a good idea to practice some of these problems. It helps children to build a better understanding of addition and subtraction relationships if they see all the various ways these relationships appear in their worlds.

Tabitha herself pointed out an important principle of Talking Math with Your Kids: Many things that you hope to remember, you can remember by encountering them frequently. Tabitha has never sat down with flash cards to memorize her single-digit addition facts. Yet she is in second grade and is starting to feel confident with them.

She and I talked about familiarity—how maybe learning 5 + 3 is a little like learning the name of someone you see in your neighborhood. You don’t recognize the person as being the same person the first few times you see them. But eventually, if you see them frequently enough, you do recognize them, and you might introduce yourself. Pretty soon, you know their name. And if you just can’t seem to remember it? That’s when it’s time to drill yourself. That’s when you repeat the name over and over and over.

Starting the Conversation

Ask the questions I did. This is an easy conversation to have. If your child isn’t confident with addition and subtraction facts, ask about six in one hand instead of jumping to five in one hand. 

More broadly, look for Part-Part-Whole opportunities to talk about. This is an important interpretation of subtraction, and one that is often neglected. Examples include apples (Our fruit bowl has 8 apples—5 are red, how many are green?), pets (There are 8 pets on our block—5 are cats, the rest are dogs. How many dogs?), et cetera.

Fun with tiles

It is no secret that one of my proudest achievements is creating a lovely space on Twitter where people share stories of children’s math talk. Come read along on the #tmwyk hashtag.

That’s where I came across this tutorial-in-photos.

Math blocks how-to photos

I decided to make myself some. I modified the design a bit (but the food coloring is a genius idea! I used that for sure.)

Then I left them out on Sunday morning and waited for a child to happen along.

Tabitha making a zig-zag pattern with the math blocks

Sure enough, Tabitha began making things.

I ate breakfast in the other room.

Ten minutes later, she came in carrying two tiles, put together so that the blue triangles made a square.

Tabitha (7 years old): A square is just a diamond, but I don’t think all diamonds are squares.

Me: Can you draw me a diamond that isn’t a square?

T: The skinny ones wouldn’t be squares.

Me: Yeah. I think I get it. Draw me one, though.

She proceeded to do so. It took a couple of tries.

I lost the paper, but the result looked something like this.

Skinny diamond

Then, a few moments later she asked a new question.

T: Aren’t all 4-sided things squares?

Me: The doorway isn’t. One of those tiles has four sides but isn’t a square.

I  quickly draw a parallelogram in my notebook.

Non-rectangular parallelogram

Me: This isn’t

I drew another 4-sided shape.

Concave quadrilateral

Me: This isn’t either.

T: That has 3 corners, not 4. So it can’t be a square.

Me: Show me the three corners.

She counted the three corners that point out from the center of the shape, missing the one that points back inward. She paused.

T: Oh…four.

So What Do We Learn?

Opportunity to think about math is important. Something as simple as leaving an interesting math object out for children to play with can lead to fun math talk.

Tabitha was working on the definitions of square and diamond in this conversation, and she was paying attention to the properties of shapes. This is important work for elementary children. When children are very young—before about first grade—they are learning to identify shapes based on appearances. As they move further into elementary school, they need to start paying attention to properties—the number of sides, the number of vertices (“corners”), etc.

Starting the conversation

Make some of these tiles. The materials cost me less than $20 (mostly for the wood—I probably could have gotten it a lot cheaper), and the dying and painting took about an hour on a Saturday evening. Then leave them out.

Or leave out a bunch of squares, triangles and rectangles you cut out of construction paper (you can do this for under $3 and less than 10 minutes of cutting).

Then let the children play and be ready to talk.

 

Math in the alphabet

The children attended a well-run chess day camp this summer. Good people running things; a warm and welcoming atmosphere. Lots of varied activities to keep kids’ bodies engaged as well as their minds.

Sadly, this takes place on the complete opposite end of the Metro area from where we live. We had to drive all the way across St Paul, Minneapolis and deep into St Louis Park during rush hour. Ugh.

This led, one day, to my trying to find a topic of conversation to keep at least one of the children occupied while we drove home. I recount for you this conversation below.

Me: Tabitha. Can I ask you a question?

Tabitha (7 years old): Sure.

Me: What letter comes before I in the alphabet?

T: H. That was kind of an easy question.

I love that she has turned into a critic. If I am not challenging her, she calls me on it.

What she has not seemed to notice yet is that these questions she deems easy are just my openers for the good stuff.

Me: Yeah. Here’s a harder one. What letter comes two letters before S?

There is a fairly long pause here. This is a harder question because of how most of us know the alphabet—forwards. If we want to know what is 2 less than 71, it is not so hard to count backwards. We have lots of experience counting backwards. But we don’t have so much experience saying the alphabet backwards, so we need to make up a strategy.

T: Q and R.

Letter squares for q, r and s

Me: Q is two letters before S, yes. Now you ask me one.

T: What letter comes after Z?

Brilliant. What a great question. I wish I had thought of it myself.

Letter squares for w, x, y, z and three blank squares

Me: Oooooo. Good one. I say A. I say it starts over.

T: Nope.

Griffin has been listening in but not participating. He sees his chance to get in on the action.

Griffin (9 years old): Negative A.

Me: Wouldn’t that be what comes before A?

G: No. It comes after Z. It’s negative A.

T: Nope. Not that either.

Me: OK, then. I am stumped.

T: Nothing.

Me: Huh?

T: Nothing. No letter comes after Z.

So what do we learn?

This is a more sophisticated version of another mathy letters conversation I had with Tabitha a while back. Back then, we were trying to figure out which of two letters comes first in the alphabet. Here, we are more paying careful attention to precise placement (two letters before, not just before).

The other interesting thing going on is our three different ideas about what comes after the end.

My idea: After the end, we go back to the beginning, like the days of the week.

Tabitha’s idea: There is nothing after the end. It just ends.

Griffin’s idea: The end is like zero. When you get to the end, you repeat what you already had, only using negatives.

It is OK that we didn’t resolve who is right.

Starting the conversation

About a year ago, I started making a habit of having the kids ask me the next question. I highly recommend it.

You know how your children are always testing the limits of rules in everyday life? Like you say, “Do not touch” and they see how close they can get their finger to the forbidden object without actually touching it? That is normal and necessary behavior on the part of children.

They will do it in the world of ideas, too. Tabitha did not choose “What letter comes after Z” at random. She chose it because she knew it would be interesting to talk about. It probably would not have occurred to me to ask it. Our conversation was richer because she did.

 

Pistachios

My father buys things in bulk. Not the bulk bin, dispense-a-little-bit-into-a-plastic-bag bulk. Costco bulk. Sam’s Club bulk.

The children and I spent some time with my father and stepmother (who are wonderful, loving people) at the Wisconsin Dells recently. We shared a rented condo. They brought bulk snacks.

Did you know that you can buy graham crackers in a container that holds four of the usual boxes of graham crackers?

What need does one family have with FOUR BOXES of graham crackers?

More to the point, they brought pistachios. I forget to check whether it was a three-pound bag or a four-pound bag but it was an awfully large bag of pistachios.

The image below is a small fraction of the total.

Sandwich bag stuffed full of pistachios in their shells.

While we were in the condo, Tabitha (7 years old) took her first interest in pistachios. Her brother Griffin (nearly 10 years old) has been a fiend for them for years. One day, Tabitha announced something to me.

Tabitha (7 years old): I threw out eight pistachio shells.

Me: And what do you learn from that?

T: I ate four pistachios.

Me: How do you know that?

T: Four plus four is eight.

Me: Nice. And five plus five?

T: Ten!

We carried on this vein for a little bit before we got distracted.

A couple days later, I was rushing around preparing for a work trip. Tabitha was again snacking on pistachios.

T: Is 13 an even number?

Me: No. Why do you want to know?

T: I must have counted my pistachio shells wrong. I must have missed one. So it’s 14.

Me: And what does that mean in terms of pistachios?

T: I ate 12. No. That can’t be right.

Me: Oh! I think I know how you got 12!

At this point, I was headed downstairs to get something to put in my suitcase. By the time I got back up, both of our minds were on to different things.

We never did get to a solution, nor did I find out how she got her wrong answer.

So what do we learn?

Tabitha is playing around with the every pistachio has two shells relationship. She is thinking about ratios: Two shells for every one pistachio.

A child does not need to have mastered multiplication, or fractions, or division to think about these things. I have written about ratio thinking from young children before. Ratios come naturally from repeating a process. Eating a pistachio produces two empty shells every time. Sharing candy produces one piece of candy every time. And so on.

Starting the conversation

In light of this, help your child notice for every relationships. There are four wheels for every car. There are four legs for every chair. There are two wings for every bird. Point these relationships out and have your child do the same. Consider the exceptions (have you ever seen a 3-legged chair?) Count up how many wheels there are on two cars, and on three cars.

Eat pistachios.

Postscript

I have two theories about her answer of 12 pistachios for 14 shells.

1. She tried to figure it out by thinking about 10 and 4. Half of 4 is 2. She added that back to the 10 and forgot that she still needed to find half of 10.

2. She subtracted 2 from 14.

I like theory 1 a LOT better than theory 2 because it matches the ways she has been thinking so far. Using subtraction seems unlikely when she knows this is a different sort of problem.

But of course I do not know for sure.

Dots!

The New York Times published an article about Common Core homework this week.

As is going to be the case with a news article (in contrast to say, a post on a blog dedicated to children’s mathematical ideas), one can’t really learn any mathematics from the piece. One critique got hit twice, though—that children are being forced to draw lots of dots.

Here near the beginning of the piece:

Ms. Nelams said she did not recognize the approaches her children, ages 7 to 10, were being asked to use on math work sheets. They were frustrated by the pictures, dots and sheer number of steps needed to solve some problems.

And a bit later:

Her daughter, Anna Grace, 9, said she grew frustrated “having to draw all those little tiny dots.”

“Sometimes I had to draw 42 or 32 little dots, sometimes more.”

I have no interest in picking up political issues surrounding the Common Core State Standards on this blog.

But I do think a parent frustrated by all those dots deserves an explanation of what all those dots are for.

Before we begin, please be assured that there is absolutely no mention of dots in the Common Core. What is mentioned is the array. An array is a collection of things arranged in rows and columns. We have discussed arrays before here at Talking Math with Your Kids. They are very useful tools for representing an important meaning of multiplication—that multiplication is about some number of same sized-groups.

Arrays (with dots or other things) are useful tools for making these groups visible, either actually visible or visible in the mind.

So I asked Tabitha (7 years old) to draw some dots for me.

Me: Tabitha, [neighbor girl and best friend] wants to play. Before you go outside, can you draw that picture for me? Three rows of five dots.

Tabitha (7 years old): That’s easy! Fifteen.

She is probably counting by fives here. She completes her picture for me.

Array of dots: 3 rows of 5.

I know that neighbor girl is waiting. I decide to press my luck.

Me: What if it had been 3 rows of 6?

There is a long, thoughtful pause.

T: Eighteen!

Me: How did you know that?

She shrugs her shoulders. Now is not the time to force things. Neighbor girl is waiting. So I offer a strategy.

Me: Let me tell you how I think you might know it.

T: OK.

Me: Six is one more than five. So each row would have an extra dot. That’s 15 for the 3 rows of 5, and then 16, 17, 18.

T: [smiles] Yeah.

We share a high five and she is out the door for a morning of clubhouse shenanigans in the backyard.

Quick note: Tabitha does not let me get away with stating her strategies incorrectly. I have done this before—summarized how I think she is thinking—and when I get it wrong, she objects. I am glad about this.

So what do we learn?

This is what those dots are for. They give us something we can talk about. Without those rows and columns, the conversation is so much more abstract. We were picturing those dots in our minds as we talked about counting them.

The three rows of five she drew gave us a jumping off point for imagining the three rows of six we discussed. Three groups of five now has a relationship for her to three groups of six.

More importantly, the strategy of finding new facts based on old facts (here that 3 groups of 6 is 18 based on knowing that 3 groups of 5 is 15), has been introduced explicitly. It is something we will talk about in the future, and something she will know to consider.

Without the array, it is not at all clear to me that she would have been able to know what 3 groups of 6 is. She could have drawn 3 unorganized groups of 6, I suppose, and counted them individually. But this is a much less sophisticated strategy, and she is ready for more than counting individual objects.

Starting the conversation

Many children do not naturally see rows and columns. Given an array, they may haphazardly count the objects around the edge, then in the middle. This often leads to double counting and skipping things.

But even children who are very good at keeping track of their haphazard counting—and who can get correct counts every time—may not see the row and column structure of an array.

So put 15 pennies in 3 rows of 5. Have your child count them and notice whether she counts in rows and columns, or whether she counts in some less structured way. Model the counting yourself so that she can see an example of the rows and columns at work. Don’t worry if she doesn’t see the structure yet, but do make a note to do more of this kind of counting in the future—seeing the structure of an array is an important stepping stone to multiplication and to the measurement of area and perimeter.

Then have your child put things in rows and columns.

Or just have her draw dots.

 

Nights of camping

The following conversation took place in the run-up to our annual summer camping trip recently.

Rachel has no interest in camping, so this ritual is all mine. I started the little ones young with a one-night trip within an hour from home so that we could come home if it’s a total disaster. As they have aged and we have developed our routines, we have gone further afield, exploring wide-ranging Minnesota state parks for two-night stays. We added a weekend fall trip, too.

Last summer, the kids began to ask why “we only go for two nights”.

Ladies and gentlemen, when the kids ask that question, you know you’re doing it right.

So this summer we are expanding to three nights. Tabitha was thinking about that change the other day.

I am straightening some things on the front porch, sweeping and tidying. Not thinking about anything in particular.

Tabitha (7 years old): If we’re going for three nights, is that 2 days and 2 half-days?

Me: Yes.

A few seconds pass.

I realize that I have an opportunity here.

Me: How did you think about that?

T: Every night is a day, except the last one, when we go home.

Me: What if we went for a whole week’s worth of nights? What if we went camping for 7 nights?

T: Easy. Six days.

Me: And?

T: Two half-days.

Me: OK. Ready for a hard one?

T: Yeah!

Me: There are 365 days in a year. So what if we went camping for 365 nights?

T: [slowly] Three…hundred…sixty…four!

Me: Nice!

T: I can even do 400.

Me: You mean 400 nights of camping? You know how many days that would be?

T: Yeah.

Me: All right. Tell me.

She does.

Later, she is in the shower. I am not-so-closely supervising nearby. I get an idea.

Me: Tabitha, what if we wanted seven days of camping?

T: How many nights?

Me: Right.

T: Eight. Am I right?

Me: I can’t trick you at all, can I?

T: Ask me another!

Again, a sign that things are going well. Contrast with her claim a couple years back, “Sometimes I don’t want to tell you about numbers because it’s just going to turn into a big Daddy math talk!”

I have to think hard to dig up something that will be more challenging for her.

Me: You want a hard one? A really hard one?

T: Yes!

Me: Last year, we went camping twice. Altogether, we camped 4 nights. How many days did we have?

T: Three…five…

It turns out that Griffin is lingering in hallway outside the bathroom. He chimes in.

Griffin (9 years old): Four.

Me: Two days, and four half-days.

G: Right. That’s four.

Me: But she’s thinking about it as four half-days, since they aren’t attached to each other. I can see an argument either way.

This summer’s trip was to Lake of the Woods in the far northern reaches of Minnesota.

Griffin posing with an oversized walleye statue in Baudette, MN

So what do we learn?

It may surprise some readers that I have filed this conversation under Algebra.

Like many of the other algebra posts, we are not using x or y, or making graphs or solving for variables. Instead we are thinking about a relationship, and about what that relationship looks like for a wide variety of numbers.

The relationship we are working with here is a simple one: one less. Tabitha had noticed that the number of full days we camp is one less than the number of nights we camp. She had even generalized the idea—notice that she didn’t count the days individually. She said, “Every night is a day, except the last one.” This answer doesn’t depend on any particular number of days; it works for all numbers of days.

What I did in this conversation was help her to apply this idea. By asking her about a wide range of numbers of days, she got to feel the power of her generalization. That is algebra.

The other important part here was continuing the conversation while she showered. Thinking in reverse is an important mathematical skill. We had started with how many days do we get with a certain number of nights? I moved us to how many nights do we need for a certain number of days? The fancy math word for the relationship between these two questions is inverse.

Starting the conversation

Camping trips, vacations, trips to grandma’s house…these are all opportunities to have the conversation we had. If your child doesn’t ask about it, you can ask your child. We are going to grandma’s house for three nights—how many days will you have to play with your cousins while we’re there?

More generally, there are two Talking Math with Your Kids moves I want to emphasize.

  1. It took me a moment to notice that Tabitha had offered me an opening for conversation. I was thinking about something else at the time. When I noticed it, I put those other thoughts aside to talk, ask and listen. That part of the conversation took probably 2 minutes. We can all spare 2 minutes to get our kids’ minds working. We just need to notice the opportunities.
  2. I followed up later on. Following up is good for two reasons: It lets you and your child examine an idea more deeply, and it helps cement memory of the conversation. We remember something we revisit multiple times better than something we only think about once.

What makes a sandwich

The 3-year old daughter of fellow Minnesotan, fellow math teacher and friend Megan Schmidt made the following proclamation a couple weeks back.

This simple claim has led to lots of fun conversation. Let’s call the daughter veganmathpup (since she is the daughter of Twitter’s @Veganmathbeagle), or VMP for short. 

All discussions with VMP are filtered through her mom via Twitter. All discussions with my own children are my best recollections of the recent silliness.

Open faced sandwiches

Veganmathpup’s assertion boils down to this: A sandwich needs these things: (1) a slice of bread, (2) a filling, (3) another slice of bread. I wanted to know about open-faced sandwiches. Is an open-faced sandwich properly called a sandwich? VMP was silent on this matter. So I asked Tabitha.

Tabitha (7 years old): That counts as a half-sandwich…actually more than a half-sandwich.

So an open face sandwich is not actually a sandwich for Tabitha. This gave me a chance to introduce the term misnomer.

Cookies

A week or so later, VMP claimed that “2, 3, 4 or 5 cookies can make a sandwich”. This was a clear violation of the earlier rule here. Two cookies, no filling? How can this be a sandwich when “It takes three things to make a sandwich”?

So I asked about Oreos. Does VMP think of an Oreo as 1 cookie? 2 cookies? Most importantly, Is an Oreo a sandwich? Megan related the following conversation.

Megan: [Handing VMP an Oreo]  VMP, I have a question.  Is this a sandwich?

VMP (3 years old):  [Examining carefully] Um, no.  It’s not.

Me:  Why isn’t this a sandwich?

VMP:  It doesn’t have things, like a burger.

Me: [Handing her two Oreos stacked on top of one another] Is this a sandwich?

VMP:  [Examining even closer this time] No.  it doesn’t have stuff in it. It needs lots of stuff inside like a burger to be a sandwich.  I want a burger.  Let’s get one [face full of oreos]. We won’t tell Daddy.

So many follow up questions I was unable to ask here. Does a Double Stuf Oreo have enough stuff inside to count as a sandwich? What about a Mega Stuf Oreo? Close up of a Mega-Stuf Oreo.

A Mega Stuf Oreo contains approximately 3.1 times the Stuf of a regular Oreo.

Marshmallows

Then the plot thickened.

Megan went on to report that, even after opening the Oreo to demonstrate that there is a filling, VMP rejected the Oreo as a sandwich because the filling is white.

Allow me to summarize:

  • Three things are required for a sandwich.
  • Unless they are cookies, in which case you only need two.
  • An Oreo is one cookie, so is not a sandwich.
  • Even if you want to call the Oreo wafers cookies and the Stuf the filling an Oreo is still not a sandwich because the filling is white.
  • The filling in a sandwich is properly referred to as a burger.

I saw a flaw in the logic, though.

Three marshmallows: mini, regular and giant

Marshmallows are white.

I asked about this. Megan reported that their marshmallows are colored.

I HAVE BEEN FOILED BY A THREE YEAR OLD!

So what do we learn?

Children have ideas.

Children use their minds. They think about things.

We can contribute greatly to our children’s learning by probing those ideas.

Formulating precise definitions is an important part of doing mathematics. Sorting things into examples and non-examples is part of this process. It really doesn’t matter whether we are sorting shapes (square, not square) or food (sandwich, not sandwich). And when the child is three years old, it really doesn’t matter whether she is consistent in her sorting.

What matters is that she is thinking in this mathematical way.

Starting the conversation

You can do as I did. Tell your child that another child says it takes three things to make a sandwich. Ask your child whether she agrees. Then ask about open face sandwiches and about Oreos.

But the bigger picture is important here too. There is a useful habit to develop as a parent—ask follow up questions when your child makes proclamations.

Other conversations we have had in this vein include Spirals, Circles and Armholes.