A short instructional video (presenter Ben) teaching the constant ratio method for mental division. The video introduces the idea via paired whole-number examples that share the same quotient (100÷10 and 10÷1; 12÷2 and 36÷6), then shows how applying the same scale factor to both dividend and divisor simplifies harder cases with decimals (3 ÷ 0.6 → 30 ÷ 6) and money (converting £1.50 ÷ 5 to 30 pence by scaling to £3 ÷ 10). The presenter includes classroom prompts to encourage student exploration.
Chapters
Hi, my name is Ben, and in this video I'm going to be showing you how to divide mentally using the constant ratio method. This is a really valuable method for dividing mentally, especially when we deal with decimals, as we will later. Okay, we have two questions. 100 divided by 10 equals 10, and 10 divided by 1 equals 10. Now it's useful to ask the children what they notice. It's different, it's the same. Hopefully they'll tell you the answers are both the same. And then it will take a little bit of probing to go a bit deeper. And they should be able to see that 10 is 10 times smaller than 100 and that one is 10 times smaller than 10. They've both been reduced by the same scale factor and that's the constant ratio method. Let's look again. Here we have two other questions, a little bit trickier, but again the answer is the same. So we have 12 divided by 2, which equals 6, and 36 divided by 6, which also equals 6. This time get the children to explore the numbers and see what they can talk about in their partners and see what happens. And they can see that now that 36 is 3 times larger than 12 and 6 is 3 times larger than 2. Now we can get into the decimals. At first glance, this question, 3 divided by 0.6, which equals 5, is taxing and a lot of children will be scared by that at first. Let's play around with the numbers. Let's increase them by a scale factor and it will help. So Here we multiply 3 by 10 to get 30, and we multiply 0.6 by 10 to get 6. 30 divided by 6 is a much friendlier equation and the children will be able to solve that one straight away. And they can see that by using the constant ratio and the same scale factor, they get the same answer of five. Finally, one more let's look at involving money questions. So we have 1 pound 50 divided by 5 equals a number. And we have 3 pound divided by 10. If you ask children which of the two they would prefer, they would prefer the bottom one divided by 10 is a lot easier. And you can see that to get from 1 pound 50 to 3 pound, you double it or you times it by 2 and therefore the constant ratio, we do the same here. So we look at 5 times 2 to get 10. And now we've got 3 pound divided by 10 is 30 pence. And the same for 1 pound 50 divided by 5. What you have to do in money is you have to make sure that it's 30 pence rather than 0.3. And that's how you can use the constant ratio method to solve division problems.
