The number line · 跟马丁学编程

Numbers lined up on a line. You can see what is bigger, what is smaller and what sits next door.

Numbers live on one line

Picture a long straight line. There are dots on it. One number lives at each dot. Zero, one, two, three… nicely in order. That is called a number line.

It is like a street with little houses. Zero lives at the start. The further you go to the right, the bigger the numbers you meet.

The number line is a great helper. You can see at once which number is bigger — the one that is further right. You can see neighbours too: next to five live four and six.

What is it for? The line turns counting into seeing. You do not have to picture numbers — you just look at them. Anyone who can draw a number line has a helper in their pocket for comparing, adding and subtracting. So today we will really get to know it.

You already know it from life. A ruler is a number line. A height chart is too. Even the scale on a thermometer. Numbers on a line are all around you.

Ema found a tape measure at home. She stretched it across the whole room. “Tereza, stand on the eight!” Tereza stands there. Ema stands on the three. “Who is on the bigger number?” Tereza looks: she is further right, further from the start. “Me! Eight is greater than three.” Then they play hopscotch: Tereza jumps from eight two numbers to the right. “Ten!” Ema jumps from three one to the left. “Two!” Jumping along the tape is really counting. They play until mum calls them for a snack. In the evening Ema draws the tape on paper with a pencil. It is smaller, but it works just the same.

💡

Right along the line = numbers grow. Left = numbers get smaller. This rule always holds.

How to read a number line

Draw your own line. It goes like this:

1. Draw a straight line. Along a ruler is fine.

2. Make ticks on it. The same distance apart. That matters — the gaps between numbers must be the same, like stairs.

3. Label the ticks with numbers. From left to right: 0, 1, 2, 3… maybe up to 20.

And now what the line can do.

Comparing: the bigger number is further right. Do you see 4 and 9? Nine is further right, so it is bigger.

Neighbours: every number has a neighbour in front and behind. The neighbours of 7 are 6 and 8.

Jumping: from a number you can jump right (you add) or left (you take away). You stand on 5, jump 2 to the right, you are on 7. We will need this jumping soon — it is the base of adding and subtracting.

Draw a line whenever you are not sure. It is a map of numbers.

Find the number 12 on the line

I have a line from 0 to 20. I am looking for twelve.

I start at zero and move my finger right. I count the ticks: one, two, three… ten, eleven, twelve. Stop. It lives here.

Who are the neighbours? Just left is 11, just right is 13.

And is 12 greater than 9? I look: nine is further left. So 12 > 9. The line showed me that with no calculating.

Jump from five three to the right

I stand with my finger on the number 5.

I jump right and count the jumps out loud: six (first jump), seven (second jump), eight (third jump).

I landed on the number 8.

Watch the common mistake: do not say the first number where you are standing. A jump is counted when you land. If I said “five” already at the start, I would get seven, and that would be wrong.

⚠️

When you jump along the line, do not count the spot you are standing on. You say the number where you land. Otherwise the result comes out one too small.

Play it

Before you go to the sheet, try it with your eyes. This is not a test — it is a game. Tap until you see it.

Practice: now you do it 🎲

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

Tap along the line. Jumping right is plus, left is minus.

Practise the questions

On paper

Paper, a pencil and a ruler. You will draw your own map of numbers.

Draw a number line from 0 to 20. Make the ticks the same distance apart.
Mark the numbers 3, 11 and 17 in colour. For each one, say both neighbours.
Jump with your finger from 6 four to the right. Where did you land? Write it down.
Jump from 14 five to the left. Where did you land? Write it down.

Now you 💪

I can draw a line with the same gaps between numbers.
I know that the bigger number is further right on the line.
I can jump from a number a few spots right and left and say where I am.

✅

Done when: You have a number line to 20 drawn and you can find every number on it and its neighbours.

What to take from this lesson

A number line = numbers lined up on a line.
Right, numbers grow. Left, they get smaller.
The bigger number is further right.
Every number has neighbours: one less and one more.
Jumping on the line is the base of adding and subtracting.