Missing Addend Addition with LEGO

We hit a wall in math.  It happens – walls, I mean.  There are some subjects that you just hit a wall (mine was chemistry in school).  But what I’ve learned since becoming a homeschooler, is that there are ways around every wall.  Up, down, around, through – there are many many ways to break down that way.  Sometimes the trick is just finding the right method.

 

If I’m being honest that method, for us, is almost always LEGO.  I think there’s a reason too.  First, LEGOs are fun.  And because they’re tied with positive emotions, when I bring out the LEGOs during math, they have an almost relaxing quality.

Second, LEGOs are hands on.  Math can be very abstract but we can make it concrete.  LEGOs are great for concrete.

 

We have more reason for using LEGOs but those are the big two.

 

Today we’re talking about missing addends with LEGO.  Addends are the numbers you add together to get the sum.  So in 2+4=6, 2 and 4 are addends and 6 is the sum.

 

Missing addends are basically subtraction problems masquerading as addition problems.  Subtraction is a tricky little bugger like that.

 

I think manipulatives are necessary when teaching missing addend.  Otherwise I’ve noticed a lot of blank stares as to why we use subtraction with an addition problem.

 

How to Teach Missing Addend with LEGO

We use LEGO with missing addend in two different ways.  First, we use the same colors for addends and the sum.  This helps with the visualization.  So here they can see the orange addend and the orange sum.  What’s missing?  The red in the sum!

 

It’s all too easy to match a few red pieces and put them in the other addend place.  Make sure to write down the equations somewhere so they can see what they’ve done.  I’d even narrate at this point:

“I have 2 orange and some red and that equals 4 LEGO pieces.  If I take away the two orange pieces, how many do I have left?  2 red pieces!”

Step it Up a Notch

Once that step is mastered we can get a little more abstract.  The sum will now be a different color.  This makes it a bit more tricky and they cannot just see the answer.  They will have to walk through it.  So put a few of one color in one addend spot and with another color, put some in the sum spot.  Then have them figure out how many are missing.

 

Again, they should say something like “There are 3 yellows and some gray that equal 5 blue.  If we take 3 yellow from the blue, how many are left?”

And that’s it!  That’s simple!  In my experience, at this point they are more than ready to understand and complete missing addend questions on paper – in the more abstract way.  This method helps them to understand what they are doing and why it works that way.