Splitting numbers · Martinとコード

Split a number into bits

Seven sweets for two friends. How to share them? Maybe 3 and 4. Or 5 and 2. Or 6 and 1. You are doing a number split — splitting into two bits.

You have already used splitting in secret. When crossing ten you split five into 2 and 3. Now we will look at it properly.

A split is drawn as a house. In the roof you write the whole number. In the two rooms under it, the bits. Roof 7, rooms 3 and 4. The bits together must always make the roof.

Almost everything can be split. Biscuits between friends. Players into two teams. Crowns into two pockets. Maths just gave it a name and a picture — a house. Today you will draw houses, fill them and learn to live in them.

Anyone who knows splits by heart counts in a flash. They see 9 = 5 + ? and know at once: 4. No fingers.

Jonáš and Sofie got 8 biscuits from grandma to share. “Half and half!” wants Sofie. They deal them: one for you, one for me. Each has 4. “Eight is four and four,” Jonáš writes in a house. Then Filip comes too. “And if we three share?” They try: 3, 3 and 2. Sofie draws a house with three rooms. “A number can break in lots of ways,” she says. “The main thing is that no biscuit gets lost.” They add the rooms out loud to be sure: three, three and two is eight. Nothing got lost. The house holds — and the biscuits disappear only after snack.

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The bits together must make the whole number. Always add it back — that is the check of a split.

Houses and filling in

How to draw a house: roof at the top with the whole number, two rooms below. For example roof 6. In the rooms you can write: 1 and 5, 2 and 4, 3 and 3, 4 and 2, 5 and 1. Also 0 and 6 — one room can stay empty.

How to find all the splits: go in order. In the first room write 0, 1, 2, 3… and work out the second room. Then you will not miss any split.

Filling in: often you know the roof and one room. 9 = 5 + ? You ask: five and how many is nine? I count from five: six, seven, eight, nine — four jumps. 4 is missing.

The most important houses are the ten houses: 10 = 9 + 1, 8 + 2, 7 + 3, 6 + 4, 5 + 5. You already know them from crossing ten. Learn them so that if someone woke you at night you would still rattle them off.

Splitting works with bigger numbers too: 15 = 10 + 5. That is a split into tens and ones — we will need that a lot in the next lesson.

All the houses for the number 5

The roof is 5. I go in order, first room from zero:

0 and 5. Then 1 and 4. Then 2 and 3. Then 3 and 2. Then 4 and 1. Then 5 and 0.

Check of each: 0 + 5 = 5, 1 + 4 = 5, 2 + 3 = 5… all match.

Six houses. None is missing, because I went in order and skipped no number.

Fill in: 8 = 3 + ?

The roof is 8, 3 lives in one room. How many live in the other?

I ask: three and how many is eight? I count from three: four, five, six, seven, eight. Five jumps.

5 is missing. So 8 = 3 + 5.

Check: 3 + 5 = 8? Yes.

Another path: 8 − 3 = 5. Filling in and subtracting are siblings — they lead to the same number.

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The most common mistake: the bits do not make the roof. You write 7 = 3 + 5 and you do not notice that 3 + 5 is 8. Add every house back.

Practice: now you do it 🎲

Now try it for real. You will see all the questions at once, like on paper. スタート with ten. If it goes well, add more.

Fill in the missing bit. Numbers to 10.

Practise the questions

On paper

Paper, a pencil and a handful of sweets or beans for sharing.

Draw all the houses for the number 6. Go in order from zero.
Fill in the rooms: 9 = 4 + ?, 10 = 7 + ?, 8 = 8 + ?.
Take 10 beans and share them into two bowls in five different ways. Write each one.
Write all five ten pairs by heart: 9 + 1, 8 + 2, 7 + 3, 6 + 4, 5 + 5.

Now you 💪

I can draw a house and find all the splits of a number.
I can fill in the missing bit: 9 = 5 + 4.
I rattle off the ten pairs from my head.

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Done when: You draw the houses for 7, no split is missing and all of them add up.

What to take from this lesson

A split = breaking a number into bits.
The bits together must make the whole number. Always check.
House: the roof is the whole, the rooms are the bits.
Filling in (9 = 5 + ?) is subtracting backwards.
Ten pairs are the base of fast counting.