Which one doesn’t belong? 1

OK, mathematicians, have you got your eyeballs ready? Great.

What do you notice?

OK, so you can see 4 dominos, look. 1, 2, 3, 4.

And yes, I see this too. They each have a different number of dots. Look, this one has 8. This one has 11. Yes, this one has 5 and this one has 3.

So if you had to make an argument or a case for why each domino doesn't belong who would you argue for, does not belong? What are you thinking? So this would be a good time to get out your paper and pencil and see if you could write down an idea for why each one of those dominoes, you think, oh sorry, why one of those domino's doesn't belong. And then yes, I know we're going to ask this question. Can you make a case for why each domino doesn't belong?

Oh yes, some are trickier than others, aren't they? Shall we have a look together? Okay. So, what about this one? What's one reason why this one doesn't belong? OK, yes, it's, oh I almost said it's the only domino with three on it, but it's not actually. But what I do notice is, it's the only domino that shows zero and some more. Did you think about that too?

Oh, you had a different reason for why that one, that's really cool. Keep ahold of that. You'll need it later.

What about this one? What's the reason why this domino doesn't belong? Ah yes, I noticed the same thing that some of you noticed. And that it's the only one that shows a doubles fact. Yeah, so it shows a double. Double 4 is 8. Mm-hmmm. Ah, there's more reasons. Hold on to them. We will come back.

OK, what about, oh this one? Yes, look, this one shows a near double. Double 2 and 1 more is 5. Ah yes, you're right, but this one is a near double too. Double 5 is 10, then one more is 11. OK, so this one doesn't work.

Why else might 5 not belong? What are you thinking? Ah OK, yes, lots of different answers, but some of you are thinking this as well. It's the only one that's half of 10. 3 is less than half of 10. 8 is more than half of 10 and well 11 is more than 10 in total.

Oh OK, you want to come back to 8 to talk about this? Yes, it's the only one that shows an even number 'cause all of the other numbers are odd. Yeah, 3 is an odd number because if I halved it, I'd have one leftover. 11 is an odd number because if I halved it there would be 1 left over. And 5 is an odd number because if I halved it there'd be 1 left over.

OK, So what about 11 then? Well, we worked out that it's odd, but so is 3 and 5. They're both odd.

What's a reason? Ahah, I hear you. It's the only two digit number. Ah, that's really nice. So can I make a case now for why each one doesn't belong? Yes, we did that, so well done mathematicians and there might be some other reasons we could have used, so it's back to you to see if you can come up with some other reasons.

Then ask your family or your friends or your classmates about the next diagram and see if you can work together to come up with a reason why each collection or image is the, is the one that doesn't belong. Yeah, I know it's gonna make your brain sweat. Over to you, mathematicians.