How To Use Bridging To Support Mental Addition And Subtraction

Hi, I'm Rebecca and in this film we're going to look at how to use bridging to support mental calculations. It's really important to remember that if you're expecting children to bridge through 10 and 100, that they actually have a good understanding of number bonds to 10 and 100 and equally that they can partition one and two digit numbers in different ways. So let's have a look at a problem. Here we have the calculation 28, 7. We could ask pupils how they might solve it and lots of pupils might choose to add one at a time and count in ones till they add seven on and that will give them the right answer, but it's not very efficient. So let's look at a better strategy. I can use this by partitioning my seven and using number bonds. So I know that to get to 30 I need to add two. So I'm going to do a jump of take. And that will take me to 30. So I've used two of my seven and I know that five and two make seven. So I know that I now need to do a jump of 5 and that will take me to 35, which will quickly show me that the answer is 35. We can also use this to do subtraction. Here I have 92 take away six. I know that if I jump back and take away two, it will take me to my bridge, my stepping stone of 90. So I'm going to take a jump back, take away two, that will take me to 90 and my number bonds to six. I know that two and four are six, so now I need to take away four, so I'm going to do a jump of four back and that will take me to 86. So quickly I have worked out that 92 take away six is 86. Let's look at a harder one. Here I have a three digit number, add a two digit number and we can do this in the same way. So this time I'm going to partition and I'd be asking pupils, well, how many more would I need to add on to get from 287 to 300? So pupils are going to need to do a jump of 13 to take us to 300. To get 15, I need another two more. So I'm going to do a jump of two and that will take me to 302 and that's bridging for addition and subtraction.