How To Use Ratio To Scale Drawings

Hi, I'm Clare and we're going to look at how to use ratio to scale drawings. Well, the way I'd start is by showing the children a diagram like this, where I've got three shapes A, B and C. And ask the children the key question, what's the same and what's different? And I'd give children a minute or two with their learning partner to have a look and to discuss this. I'm hoping that they're going to see that these three shapes, they are all squares and you can see that looking at them, they might point out the fact that they're the same colour, but you can see that shape A is half the size of shape B and shape B is half the size of shape C. Okay, now, when I'm looking at that from point of view of ratio, the ratio from A to B and from B to C is going to be one to two, because they are twice as big as each other. When I look at the ratio of square A to square C, it's going to be one to four, because I have to multiply the sides of shape A by 4 to make the square shape C. Right, let's look at this question. It's quite different. I've got shape D and E. Shape D. If I look at it, I can see it's smaller than shape E. D has been enlarged into shape E and I can see that the rectangular shape E has one length of 4 cm and the longer length is 8 cm. Let's have a look at the question. How can we work out the dimensions of shape D if shape E has been enlarged by a scale factor of 4? So this time, instead of asking the children to start with the small shape and work out what an enlargement would be, we're going to do the opposite and we're going to reduce it. So I want to reduce shape E by a scale factor of 4. So I'm going to divide the sides by 4. I'm looking at the short side first. 4 cm divided by 4 will give me 1 cm and 8 cm divided by 4 is going to give me 2 cm. So there we have it. That's how we use ratio to work out the scale factor of drawings.