About this video
A tape diagram shows 12 parts yellow paint and 8 parts red paint. The video finds the ratio of red paint to total paint (8:20), then splits both colours into 4 equal groups to show the simpler equivalent ratio 2:5.
You'll be able to
- find the total in a ratio problem by adding all the parts.
- tell the difference between a part-to-part ratio (red to yellow) and a part-to-whole ratio (red to total).
- use equal groups in a tape diagram to simplify a ratio.
Key words
- tape diagram
- A drawing of strips split into equal parts, used to show and compare amounts.
- ratio
- A comparison of two amounts, such as 8 parts red to 20 parts total, written 8:20.
- equivalent ratio
- A ratio that shows the same relationship using different numbers, like 8:20 and 2:5.
Transcript
- [Instructor] We're told that the following diagram describes the volume of yellow and red paint in an orange mixture. So we can see that for every 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 parts of yellow, we have 1, 2, 3, 4, 5, 6, 7, 8 parts of red. They ask us, "What is the ratio of red paint to total paint in the mixture?"
So, pause this video and see if you can have a go at that before we do it together. All right, so if we wanna think about red paint, it looks like we have every, we have eight parts red paint, and if we think about the ratio of that towards total paint, you might be tempted to put a 12 there.
But that's not the total paint, that's just the yellow paint. The total paint for every eight parts red, would be the eight parts red plus the 12 parts yellow. So, it'd be eight plus 12, which is 20. And this is true, the ratio of red paint to the total paint in the mixture is 8:20.
Now, you might not always see it expressed this way, because there's other ways of writing an equivalent ratio. Some that people would argue are actually simpler. Another way to think about it is this diagram where we see the red paint, it has eight parts right over here, but we could also describe it as four groups of two.
Just like that, because eight is divisible by four. And if you divide the 12 parts of yellow into four groups, it's four groups of three. And you'll see in a second why this is really interesting, because we were able to break down both of these into four groups.
And when you do that, you see very clearly, hopefully, that for every two parts of red you have three parts of yellow. For every two parts of red, you have three parts of yellow. Two parts of red, three parts of yellow, and then last but not least, these two parts of red and then those three parts of yellow.
So, for every two parts of red you have three parts yellow. Now once again, the ratio that they're asking isn't the ratio of red to yellow, which is two to three, but you could just take one of these groups and say, all right, for every two parts of red I have 1, 2, 3, 4, 5 parts of total paint.
So, you could say that the ratio is also, for every two parts of red, I have five parts of total paint. And hopefully, this makes intuitive sense right here. Why these two things are equivalent. If for every eight you have 20 total, well, if you divide that by four for every two of red, you're going to have five.
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