Bài 15: Subtracing using number – line

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Starry, I notice you like play with your number beads.

oh, And you have learnt to use them to make the number line .Good!

As I told you the number line is useful to us in many ways.

Today I will show you how you can do subtraction with the number line.

You do remember how to draw the number line Starry?

Yes, 2 arrows on each the side with numbers 0-1-2-3-4-5-6-7-8-9 and 10 written at equals distances.

Let us take 5 minus 2.

Look at the number line and start from 5, do subtract 2, we move 2 places to the left.

1-2, we reach the number 3.
So 5 minus 2 is 3.

You look happy Starry, that’s easy, isn’t it?

What about 6 minus 4?

Start from 6, we move 4 places to the left 1-2-3-4, we reach the number 2.

So 6 minus 4 is 2.

Here is 4 minus 1. Start from 4, we move 1 place to the left ,we reach the number 3. So 4 minus 1 is 3.

Let’s us now do an activity together!

We have to first subtract by crossing out the objects and next carry out the subtraction using the number line.

Shall we begin!

First we have the kites.
1-2-3-4-5-6-7-8 kites minus 1-2-3 kites that 8 minus 3 equals 1-2-3-4-5 kites.

Now using the number line, start at 8 move 3 places 
To the left 1-2-3, we reach the number 5.

So 8 minus 3 equals 5.

Next the balls 1-2-3-4-5-6-7 balls minus 1-2-3-4-5 balls that 7 minus 5 equals 1-2 balls.

Now using the number line, start at 7 move to 5 places to the left 1-2-3-4-5, we reach the number 2.

So 7 minus 5 equals 2.

Now, look at the tops 1-2-3-4-5 tops minus 1 top that 5 minus 1 equals 1-2-3-4 tops.

Now using the number line, start at 5 move 1 place to the left, we reach the number 4.

So 5 minus 1 equals 4.

And now the marble , Starry! 1-2-3-4 marbles minus 1-2-3 marbles that 4 minus 3 equals 1 marble.

Now using the number line, start at 4 move 3 places to the left 1-2-3 , we reach   the number 1.

So 4 minus 3 equals 1.

So Starry the number line is useful for both addition and subtraction.

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