This content was created by Rob Langman. This content was uploaded by Rob Langman. This is a YouTube instructional video titled "Using A Comparison Bar Model To Find Unknowns In Fraction Problem" (created 2024-04-03). The single speaker, Claire, presents a primary-school math lesson demonstrating how to use a comparison bar model to solve a fractional relationship problem. Using an example about Fred and Harry's pumpkins (total 72 kg) she shows that 3/5 of Fred's pumpkins equals Harry's weight, models Fred as 5 equal parts with Harry matching 3 parts, gets a total of 8/5 = 72 kg, so one-fifth = 9 kg, yielding Fred = 5×9 = 45 kg and Harry = 3×9 = 27 kg. The clip is an explanatory teaching segment aimed at children, focusing on visual bar-model methods and checking answers.
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Hello, I'm Claire and today we're going to have another look at bar models and how to find an unknown quantity when we've only been given the fractional relationships. Okay, let's have a look at the question. This one's all about Fred and Harry, who've been growing some pumpkins. Okay. It says three fifths of Fred's pumpkins weigh the same as Harry's pumpkins. The total weight of their pumpkins is 72 kg. What is the weight of the pumpkins that each boy has grown? It sounds quite complicated, but when you draw it it looks much, much simpler. Ok, let's have a go. We've got three fifths of Fred's pumpkins weigh the same as Harry's son. And I'm going to start by drawing Fred's pumpkins. So here's a bar that's going to represent Fred. Now it says 3/5 of his pumpkins are the same as Harry's. So I'm going to divide that bar into fifths by drawing four lines. Two, three, four. Now I'm going to draw Harry's pumpkins and Harry is exactly the same as three fifths. So I'm going to put Harry underneath so he matches up exactly to Fred's three fifths. So there is Harry. Okay. I'm also told in this question that the total weight of pumpkins is 72kg. So I'm going to put that on as well. So I know that both together it weighs 72 kg. Okay, I've put that in the corner there. Right. So now I can have a look at it. I can see that together they have 1, 2, 3, 4, 5, 6, 7, 8/5. So I've got 8/5 which make 72 kg. At this point I would ask the children, if I know that 8/5 are 72, how can I find one fifth? And I would hope that they'll be able to tell me to find one fifth. I need to do 72 divided by eight, which will give me nine kilograms. So I'm going to put that down there. I'm now going to draw that on my bar model. So each of my fifths here is going to represent nine kilograms. Now, the danger is once children have done this, they think they've completed the task. But you need to tell them to go back and check they've answered the whole question. So let's have a look again. At the end of the question it said, well, what is the weight of the pumpkins that each boy has grown? Right. I need to look back at my bar model now. Okay. Fred, he had five. Five fifths, okay? And each one is nine. So Fred has five lots of nine kilograms. So he has 45 kilograms of pumpkins. Let's do Harina next. And when I look at Harry, he's got three lots of nine, so he's got 27 kilograms. It's always a good idea, once children have worked that out, to get them to check their calculations to make sure it's correct. They can do this by looking back to see they should add up to 72. So let's do that. Let's do 45, add 27, and we can see that does make 72 kilograms. And there we have it. That's how we use a bar model to find an unknown quantity. When we've been given the fractional relationships.
