# MathsClass

A blog about teaching and learning in a maths classroom.

## Double Strength Cordial and Ratio

Tuesday, 18 January 2011 | 6 Comments

When introducing the topic of ‘ratio’, I use the mixing of cordial as an illustration that most kids get.
The idea of using 1 part of cordial to 4 parts of water makes sense to them – and they get the idea of equivalence when you mix the cordial in a different sized container (I use the examples of using cups to fill a bottle for a picnic, and using buckets to mix a big batch for a party).

Recently Cottee’s Cordial started making their cordial concentrate in 1 L rather than 2 L bottles.  Doubling the strength of the concentrate with the instruction, “Just Use Half”.  See ‘Products’ on the Cottee’s Cordial web-site.

Rather than explaining how I’m thinking of using this in class – because to be honest, I’m not sure – I’m going to pose a WCYDWT? ala Dan Meyer.

So, what can you do with this? Your suggestions in the comments.

### 2 L Bottle

(click on images to view larger)

### 1 L Bottle

A set of photos is in the zip file below. High resolution versions are available on Flickr.

Cordial ZIP, 754 KB

Posted in • Lesson IdeaRatioMediaPhotoWhat can you do with this? | Short URL: http://mths.co/2097

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Nordin Zuber on  18 January 11  at  10:49 AM #
Adam Bevan on  18 January 11  at  08:43 PM #
Deb Hogg on  18 January 11  at  09:41 PM #
These previous two comments are such fun! Good job guys! Strange that as soon as product changes and value for money get mentioned, my housewife hat goes on and I think... toilet paper! Could just imagine bringing in different rolls and comparing sizes of sheets and length of rolls and all those other value for money concerns! Now there's a class you would have to have a great relationship with - the class where you can discuss toilet paper!

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Simon Job on  20 January 11  at  08:44 AM #
Thanks for the great ideas. @enzuber Home Brand - I like the non-natural flavours of my childhood. I'm a devotee of green snakes, green jelly beans and green frogs. I lament the move to natural flavours 😊 @Adam Bevan, thanks for the ads, my daughter loved them 😊 I use that video about Cadbury packaging when looking at "Surface Area":http://mathsclass.net/comments/surface-area-and-chocolate. @Deb Hogg - toilet paper - love it. Best Buy in Year 9/10. One of my first thoughts was looking at the recipe for the new concentrate - 1:9. It just looks wrong. The original recipe is 1:4, the new recipe is double strength, so shouldn't it be 1:8? I look forward to taking all these ideas and putting into a lesson later this year. Thanks.
Peter Gould on  23 January 11  at  01:17 PM #
Your comment: "One of my first thoughts was looking at the recipe for the new concentrate – 1:9. It just looks wrong. The original recipe is 1:4, the new recipe is double strength, so shouldn’t it be 1:8?" I think that you could ask that question of Year 8 or Year 9 as a discussion starter. But be prepared for the misconceptions that will come up and allow time to resolve them. This is potentially quite a nice idea to discuss the difference between ratios and fractions. Comparing 1/5 (original) to 1/10 (new) and what might the 1 in the numerator represent? I would expect to see some drawings in the explanations. I use the 'concentration model' with fractions but I don't think that it is commonly used.
Nan on  09 March 11  at  08:09 PM #
I would be telling the class that the reason Cottees is selling the smaller, more concentrated cordial, is because they are using an artificial sweetener (sucralose) so that they can use less natural sugar. What they don't tell you is that sucralose is a chemical manufactured in a laboratory, it is very close to those chemicals called aspartame, and that aspartame is banned in many countries. They also don't say that sucralose is experimental in nature and they don't yet know what the effects on humans are. Maybe a class in ethics in marketing should be on the agenda.

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Simon Job — eleventh year of teaching maths in a public high school in Western Sydney, Australia.
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