Question Video: Representing Three-Digit Numbers on Number Lines | Nagwa Question Video: Representing Three-Digit Numbers on Number Lines | Nagwa

# Question Video: Representing Three-Digit Numbers on Number Lines Mathematics

Which arrow is pointing at the number 670?

05:02

### Video Transcript

Which arrow is pointing at the number 670?

We’re given five different number lines here. And can you see? On each one, there’s a blue arrow pointing out a position. But only one of the blue arrows is pointing where the number 670 belongs. Let’s go through each number line to try to find out which one it is.

Now, if we look at our first number line, we can see that not all the marks on the number line have got a number by them. We start with the number 600. Then we make one, two, three jumps before we get to the number 630. Now, we know 630 is 30 more than 600, and 30 is the same as three 10s. So each jump that we’ve made must be worth 10. 600, 610, 620, 630. The numbers fit. And we’ve worked out that the scale of the number line is to count in 10s.

Let’s count on in 10s from 660 to find out what number the blue arrow is pointing to. 660, 670. This is the number we’re looking for, so we can see straightaway that the arrow isn’t pointing to it. And then 10 more than 670 is 680. The first arrow doesn’t show 670; it shows 680.

Let’s try looking at our second number line. This number line is a little bit similar to the first one in that the first number we can see labeled is 600 and the last number is 690. But we can see that there are a lot more notches on this number line, aren’t there? The scale must be different.

Let’s try and work out what the scale is. If we start at 600, we make one, two, three jumps before we get to 615. Now, on the first number line, we made three jumps and we got to 630. That was by adding 10 each time. But this time, we’ve only got to 615. So it seems like we’re adding less than 10. Let’s try counting in fives. 600, 605, 610, 615. It works! And so we know that, on this number line, each interval or mark is worth another five.

Now that we’ve worked out the scale of the number line, we can work out the value of the arrow. Is it pointing to the number 670? Let’s start with 660, which is the notch before it, and we’ll count in fives. 660, 665. Oh dear, we can see that the number the other side of the arrow is the one we’re looking for, 670. On this number line, the arrow is pointing to 665, not 670.

This next number line is a really quick one to understand. 100, 200, 300. We can see that the scale is to count in 100s. And the blue arrow on this number line is pointing halfway between the number 500 and 700. We know that this arrow is pointing to the value 600. We’ve only got two more number lines to look at. Which arrow is pointing to the number 670?

Now, can you see a similarity between this number line and the first one we looked at? Each of the intervals is worth 10. On the first number line, not all the numbers were labeled, were they? But on this one, they are, all except the one with the blue arrow. 600, 610, 620, 630. Just like the first number line then, we’re counting in 10s. And we can see that the blue arrow is the number that comes after 660. And 10 more than 660 is 670. It looks like this is the answer we’re looking for.

Let’s just check our final number line. Well, if we look at where the blue arrow is pointing on this number line, we can actually use some number sense to realize it’s not pointing to the number 670 at all. It’s pointing to a number that comes after 675. And because we know 675 is more than 670, we know that the blue arrow must be pointing to a number more than 675. We don’t even need to know the scale on this one. We can see straightaway it’s not going to be 670.

The correct number line is the one that shows a scale that goes up in 10s each time. And it shows the arrow pointing to the number that comes after 660. We know this because the number that is 10 more than 660 is 670.

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