How to Use Bar Modelling for a Subtraction Problem

Hi, I'm Zoe and in this video we're going to be looking at how we approach a multi step word problem involving subtraction using our bar model. So here's our problem. Simon walks into a shop and buys two books for five pound 54 each and one bookmark for one pound 24. He pays with a pound 20 note. How much change does he receive? First step would be to get the children to read this problem a couple of times and then have a chat about what it means. We're now going to start with a bar model and what we know. We know our bar is going to represent the amount of money that Simon has. He has £20 in total. We're then going to split up our bar into the other knowns. He bought two books for five pound 54, so we're going to use our bar to represent those two books for £5.54. We try to keep as much as possible the proportionality within our bar so it gives the pupils a good idea of what we're spending. He then buys one bookmark for £1 24. So we're going to have our bookmark, the bar, slightly shorter to represent £1 24. Now a discussion with the pupils about why you haven't filled the whole bar would be good. And what this represents. So what could we label this with? Hopefully they come up with the idea that this is the change that Simon's going to receive, so we can label that with our change. So what else do we know? We can now work out how much he spent in total. So we're going to work out this part of our bar. They might use the column addition method, they might use another method that you've shown them, but hopefully they arrive at the fact that he has spent £12.32. We can label that on our bar. So now what we're left with is this part, the change, and hopefully pupils will realise the whole thing's worth 20. So to work out how much change we need to do 20, take away 12 pounds 32 to get to 7 pounds 68 and that is how much change Simon receives. So we've seen here now that we can use our bar model in a complex multi step problem with subtraction to find our answer.