### Video Transcript

This line shows a sequence of whole
numbers. What numbers are missing?

The first sentence of this question
is a really good way of saying what a number line is. It’s a line that shows a sequence
of numbers or, in other words, it’s a way of showing numbers in order. And we can see with this number
line that our numbers get bigger. We start with 100, and it goes all
the way up to 900. But can you see there are two
missing numbers along the way? What are they?

Let’s look at our first number to
begin with. The first thing we can say about
this missing number is that it comes after 100. But that’s not really much of a
help. We could be counting in ones, in
which case our missing number is 101. Or maybe we’re counting in 10s. 100, 110.

To decide what our missing number
is, we need to look really carefully at our number line to see what the scale is, in
other words, to see what we’re counting on in each time. Let’s look at some numbers that are
in a row that we know already. 300, 400, 500, 600. Can you spot what we’re counting
in? This number line shows jumps of
100. So if we go back to the very
beginning and we start with 100 and make a jump of another 100, we can see that our
first missing number is going to be 200. And this fits in with the sequence,
doesn’t it? 100, 200, 300, 400, 500, 600.

What’s the next missing number
going to be? What’s 100 more than 600? It’s 700. Let’s count along the whole number
line. 100, 200, 300, 400, 500, 600, 700,
800, 900. We worked out that the scale of
this number line was to count in 100s. And that’s how we know the two
numbers that are missing are 200 and 700.