# Subitising 6 (one less than)

A thinking mathematically targeted teaching opportunity focussed on using mathematical imagination to visualise numbers being taken away

## Syllabus

Syllabus outcomes and content descriptors from Mathematics K–10 Syllabus © NSW Education Standards Authority (NESA) for and on behalf of the Crown in right of the State of New South Wales, 2023

• MAO-WM-01
• MAE-RWN-01
• MAE-RWN-02

## Watch

Watch Subitising 6 (one less than) video (6:07).

Match a collection, numeral and word that represents one less.

### Transcript for Subitising 6 one less than video

[A title over a navy-blue background: Subitising - 5. Small font text in the upper left-hand corner reads: NSW Department of Education. In the lower left-hand corner is the white waratah of the NSW Government logo.

A large butcher’s paper covers a table. On top of the paper is a row of cards numbered and labelled from 0-10.]

### Speaker

Welcome back young mathematicians. I hope that you have had a really delightful day today. So I'm gonna do some subitising and that means that we're able to tell how many there are in a collection without having to count. And today, when we're subitising instead of just saying the number that we see. So if I saw this card…

[She puts down an orange card with 2 white pompoms in the middle.]

### Speaker

[She places a pink label above the card that reads: one less than (the number before).]

### Speaker

…what I'd like you to think about is one less than the number that you see. So the number before two. So that means in my mind I have to subitise and go, oh, there's two and one less than two…

[She covers the pompom on the right.]

### Speaker

…leaves one. Mm-hm…

[She points to the cards above.]

…and we have our cards up here too, so that when you are playing along at home, you can also point to the symbol…

[She points to the ‘1’ card.]

### Speaker

…that represents what the answer is when there's one less than or the number before what you see on these cards. Are you ready to go?

[She takes the orange card away.]

### Speaker

OK, I think you know this one.

[She holds up the orange card with 2 white pompoms in the middle. She flips it and puts it on the table.]

### Speaker

So what's one less than... Can you point to it for me?

[She points to the ‘1’ card.]

### Speaker

Did you think one?

[She flips the card right side up.]

### Speaker

Because we have two in total, and one less than two is one.

[She takes the orange card away.]

### Speaker

[She holds up a plate with 3 green pompoms.]

### Speaker

[She flips it and puts it on the table.]

### Speaker

So how many did you see? And then imagine one being taken away for one less than. Did you think two?

[She points to the ‘2’ card.]

### Speaker

Let's check.

[She flips the plate right side up.]

### Speaker

Mm-hm because there's three that we can see here…

[She traces the shape of the pompom set.]

### Speaker

…and a triangle and if we take one away…

[With her left hand, she covers the pompom on the bottom left.]

### Speaker

[She takes the plate away.]

### Speaker

[She holds up a white square with 2 black dots on a diagonal. She puts it down on the table.]

### Speaker

What's one less than this number?

[She takes the square away.]

### Speaker

One…

[She points to the ‘1’ card.]

### Speaker

…mm-hm…

[She puts down the square.]

### Speaker

…because we see two and one less than…

[With her left hand, she covers the dot on the bottom left.]

### Speaker

…or the number before two is one, OK.

[She takes the square away.]

### Speaker

[She holds up a paper plate with a purple pompom in the centre. She flips it and puts it on the table.]

### Speaker

[She points to the ‘0’ card and flips the plate right side up.]

### Speaker

…that's right because we could see one and one less than one or the number before one.

[She covers the pompom. She points to the ‘0’ card.]

### Speaker

If we take one away is zero.

[She takes the plate away.]

### Speaker

OK, here we go. Eyeballs ready.

[She puts down a pink card with 3 white pompoms on the left side and 1 pink pompom on the right.

She flips the card.]

### Speaker

What's one less than that. Were you thinking three?

[She points to the ‘3’ card.]

### Speaker

Yeah, let's look.

[She flips the card right side up.]

### Speaker

There's four here…

[She circles the pompoms.]

### Speaker

…and one less than four…

[She covers the pink pompom.]

### Speaker

…is three. The number before four is three, OK.

[She takes the card away.]

### Speaker

[She puts down a plate with 1 pink pompom on the left, and 4 blue pompoms on the right arranged like a square.]

### Speaker

What's one less than.

[She flips the plate.]

### Speaker

I should say it again, I think you're thinking four…

[She points to the ‘4’ card.]

### Speaker

…but let's check.

[She flips the plate right side up.]

### Speaker

One less than five…

[She circles the pompoms. She covers the pink pompom.]

### Speaker

…is four, that's right. The number before five…

[She circles the pompoms. She covers the pink pompom.]

### Speaker

…is four because we take one away from five and we leave four, OK.

[She takes the plate away.]

### Speaker

[She puts down a plate with 3 red pompoms running down the middle.]

### Speaker

What's one less than that many?

[She flips the plate.]

### Speaker

Two…

[She points to the ‘2’ card.]

### Speaker

…let's check.

[She flips the plate right side up.]

### Speaker

We have three.

[She circles the pompoms.]

### Speaker

If we take one away…

[She covers the bottom pompom.]

### Speaker

…one less than three is two. The number before three is two.

[She points to the ‘2’ card.]

### Speaker

[She takes the plate away. She puts down a square with 1 black dot in the centre.]

### Speaker

You ready? What's one less than that?

[She takes the square away.]

### Speaker

Zero…

[She points to the ‘0’ card.]

### Speaker

…yes, because one less than one leaves me with none which is zero.

[She points to the ‘0’ card.]

### Speaker

[She puts down a square with 4 black dots in each corner. She takes the square away.]

### Speaker

Three.

[She puts down the square with 4 black dots.]

### Speaker

Here's four, one less than four is…

[She covers the dot on the bottom right.]

### Speaker

…three. The number before four is three.

[She takes the square away.]

### Speaker

[She puts down a pink card with 1 blue pompom on the top, and 5 white pompoms below arranged like a square with a centre pompom. She flips the card.]

### Speaker

Would you like to see it again?

[She flips the card right side up.]

### Speaker

What's one less than this many? You're right, it's five.

[She points to the ‘5’ card. She circles the 5 white pompoms.]

### Speaker

Look, five…

[She circles the blue pompom.]

### Speaker

…and one more is six. One less than six…

[She covers the blue pompom.]

### Speaker

…is five. The number before six is five.

[She takes the card away.]

### Speaker

I know colour was very helpful there…

[She brings the card back.]

### Speaker

…you're right, because we could see five…

[She points to the 5 white pompoms.]

### Speaker

…on dice pattern…

[She points to the blue pompom.]

### Speaker

…and one more to see six.

[She takes the card away.]

### Speaker

OK, let's do this one, last one.

[She puts down a plate with 4 purple pompoms arranged like a square with 1 green pompom in the middle.]

### Speaker

What's one less than this many.

[She flips the plate.]

### Speaker

Can you point to it?

[She points to the ‘4’ card.]

### Speaker

Yes, it's four, one less than five is four.

[She flips the plate right side up.]

### Speaker

Look, here's five.

[She circles the pompoms.]

### Speaker

If I get rid of one…

[She covers the pompom on the bottom left.]

### Speaker

…it leaves me with four. One less than five is four, the number before five is four.

Nice subitising and thinking little mathematicians.

[Text over a blue background: What is the mathematics?]

### Speaker

OK, mathematicians, what was some of the mathematics in here?

[A title on a white background reads: What was (some of) the mathematics?

• We used our skills in subitising this time to determine relationships like:
• 1 less than
• We can describe ‘1 less than’ as ‘the number before’. It means we take one away from the collection (we can also just imagine it being taken away)

### Speaker

So we use our skills in subitising today to determine important relationships like one less than. We can describe one less than as the number before, and it means we take one away from a collection. And we can also just imagine it being taken away.

[Over a grey background, the red waratah of the NSW Government logo appears amongst red, white and blue circles. Text: Copyright State of New South Wales (Department of Education), 2021.]

[End of transcript]

## Instructions

• When you see a collection displayed in the video:

• think about how many there are without counting

• think about what one less than that value is (for example, if you see a collection of 2, one less than 2 leaves 1)

• point to or record the number.