Subtraction stacks

Alright, I'm here with one of my favourite mathematicians today, Hi Sam.

Hi Michelle.

How are you going?

Good.

Are you ready to play one of our favourite games, the counting game?

Yeah.

Do you remember how to play?

Yeah, but sometimes you loose track so maybe if we use some of these counters it might be easier.

That's an excellent idea. We could also use a ten frame.

Great.

We... our target is going to be 24 today so how many ten frames would we need?

Probably 2 then we could just put some on the side.

That makes sense because two tens is equivalent to twenty isn't it?

[Child is drawing ten frame]

Oh yeah, I can see the big rectangle, and then you partition that into two skinny rectangles. And then one, two, three, four lines in the middle will make 5 boxes on each side. You've got some knowledge about the structure of 10 frames.

[Child draws a second ten frame]

Yeah, I like how you counted to check, so if there's five on this side, what do we know about this side?

That there will still be five because it is symmetrical.

Nice, alright, so let's play. Would you like to start or shall I start?

I'll start.

OK?

So let's go one, two, three.

Ok, I think it's a good idea to get counters. I'm going to say four.

Five, six.

Seven, eight, nine.

Ten, eleven, twelve.

Thirteen, thirteen.

Fourteen.

Fifteen and sixteen.

Seventeen.

Eighteen.

Nineteen.

Twenty. Twenty-one.

Twenty-two, twenty-three, twenty-four.

Congratulations. Do you want to play again? Maybe you could play best out of three? But do you want to play going backwards this time?

Yeah, we could go backwards, forwards, backwards.

Yeah, that's a great idea.

So would you like to start or will I start?

I'll start.

OK.

Twenty-four, twenty-three, twenty-two.

[Adult stops and puts counters back]

Oh, hold on, I saw what happened there. So we had twenty-four to start with.

So at twenty-four and then you took away so we had twenty-three, twenty-two, twenty-one. It's always is tricky in the backward count? That's why the structure can really help us, yeah. You do it this time.

Twenty-three, twenty-two, twenty-one.

Yeah, nice. So sometimes Sam, I like to like take it away and then say the number so I don't get stuck. So now there's twenty, nineteen and eighteen and I can just double check, I do a quick scan in my head because this ten frame is full and there's two missing here, so it was full it would be two tens and there is two missing, so there's one ten and eight and we just recall that, we rename that 18. Alright, your go mister. I'm determined to win.

Seventeen.

Screen reads And now it's your turn to strategise and play! (and wonder... who do you think might have won?)