Once upon a time there was a rabbit who had ten bunnies. She had taken three carrots from the garden but she needed ten. In fact, she always needed ten. How many more carrots did she need in order to feed her hungry bunnies?
Your first inclination may be to subtract 10 from 3, correct? Sure… go for it!
But, what if we added a little mystery to it? You know, maybe keep the addition symbol and throw in a question mark?
I know, I know… sounds a little craycray, but hear me out.
This is how you can teach a little prealgebra to kiddos who are just learning addition.
We’ll make it a little easier, too. All of the addends have to add up to the magic number of ten. In Montessori Land, we call this Make Ten.
In Indigo Land, it’s called The Case of the Missing Addend.
Ready? Grab your colored beads and a single ten bar, and let’s do this.
Materials:

1. Colored Bead Bars
2. One golden ten bar
3. Question mark (you can draw this on a small piece of paper or cut one out of hard felt)
4. Addition and equal symbols (mine are on large, flat, clear gems, drawn with permanent marker)
5. Colored Bead Stair Journal
Procedure:
Prep Work! With the initial introduction, I’ll forgo the question mark, just to show the child how to compare the colored beads to the golden ten bar. They may also remember this if they had done previous addition work with the CBS.
With all of your materials in order, place a single golden ten bar to the right of the equals symbol.
Take one random colored bead bar from the first bead stair.
Place the bead bar on directly above the ten bar so that the beads align.
Using your pointer, start to count the beads remaining on the ten bar. Slightly exaggerate your counting of 1…2… etc.
Once you get to the last bead, accentuate the number of beads you counted. In this case, it is the number six.
Grab your six bead bar from the other colored bead stair…
And place it alongside the remaining beads. You can place it right next to the first bead bar, or underneath. Either way, it gets the job done! Start to count the beads all the way across to make sure that they equal ten. I always ask the child to double check his work.
Remove the ten bar to show your new pair…
Then show the child how it will look when placed with the symbols.
Write this problem down in the Colored Bead Stair Journal. The child can either color the beads in to match the manipulatives, or you can have the child use matching colored pencils like the one pictured above. Voila!
Now for the Case of the Missing Addend!
Place your mysterious question mark to the right of the addition symbol.
Randomly choose a bead bar from the first bead stair…
And place it to the left of the addition symbol. Your problem now looks like this. Read the problem outloud to the child, as 8 plus what equals ten? I’ll joke around a little and say something like, This mystery must be solved… what could it be?
Bring the colored bead bar, in this case it is 8, and place it above the golden ten bar as previously shown.
Pick up your pointer and start to count the remaining beads out loud – or have the child count them. Two! Could the mystery number be two? You could say.
Take the two bead bar from the other colored bead stair…
And place it above or below the remaining beads on the golden ten bar.
Remove the golden ten bar (you can place it back to the right of the equals symbol), pick up your pointer, and count the 8 and 2 bars together. Say, 8 and 2 make 10!
Set the eight bar to the left of the addition sign, then flip the question mark card over (or remove it).
Place the two bead bar to the right of the addition symbol (and on top of the card if you kept it there).
With the colored bead bars in their places, repeat the whole problem out loud and exclaim Mystery solved!
Write the problem down in your journal and clear the board.
Here’s one more for good measure…
Prep your board (work space).
Choose a bead bar.
Place it to the left of the addition symbol. Say, 9 + what equals 10?
Set the bead bar above the ten bead bar.
With your pointer, count how many beads are remaining on the ten bead bar. In this case, it’s One.
Align the one bead bar above or below the ten bead bar’s remaining bead.
Remove the ten bead bar and count the new colored bead bars, making sure they count to ten.
Place the nine bead bar to the left of the addition symbol, flip your question mark card over…
And place the one bead bar on top. Repeat the problem out loud and exclaim, Mystery solved!
Using your colored pencils, write the problem down in your journal.
You can label this work as Make Ten, Mystery Number, or whatever name you come up with that fits!
Next up: Rectangular Arrays