## K-6 Math in the News: Supermarket Math Fails

Do your students believe that math is irrelevant to their lives? Sadly, all too many of them do, especially as they reach high school.

The article I discuss this week lists 10 occasions in which major Australian supermarkets got the mathematics behind their special offers totally wrong. Sometimes the “offer” was worse than the standard price, sometimes it was exactly the same. And occasionally the offer was better than the staff member who put up the marketing ticket realised.

I love this article for its immediate relevance to students. Very few people don’t enjoy finding a bargain, but no-one wants to be ripped off. The examples here provide lots of examples for students to figure out what each offer is, what it’s really worth, and suggest a better, more honest offer.

Buyer beware! Even though stores are using computers to create special ticket offers, human beings are required to think up the actual numbers in each offer. And sadly, some staff members don’t recognize their own mistakes before letting customers find out about the specials.

### What do you think?

Do you do “shopping math” in your classroom? Share a comment below.

## Reference Article

10 Times Aussie Supermarkets Failed at Math

## Teaching a Great Math Lesson Part 1: Capture Students’ Attention!

#### Great Math Lesson Series:

 Phase I Phase II Phase III Phase IV Phase V Introduce Stimulus Whole-class Activity Problem Solving Synthesis & Reinforcement Revision & Recap

This is the first of a five-part series on how to teach a great mathematics lesson, using a simple, purposeful template that can be adapted for any math topic and any age level.

## First Phase: Introduce a Stimulus

Lots of math lessons fall down in the first ten seconds: “Who can tell me what ‘ratios’ are?” Seriously, which kid or teenager is going to want to answer such a question? Later in the lesson, there will be time for lots of questions. But ask such a question in the first few seconds? Never.

You know what they say about first impressions? You don’t get a second chance to make one. Well, it’s the same with teaching. I remember starting a lesson when I was a student teacher, saying “I’m now going to teach you about ‘protecting the environment’”, or some such thing. The children were polite enough not to groan out loud, but I could see the reactions immediately on their faces: Who wants to learn about THAT?

So, what should a teacher do?

Start with something interesting, exciting, unusual, unexpected, surprising, creative or enticing – which is connected with today’s math topic. Such as:

• Fractions – dress as a chef, bring in a chocolate cake, cut it into halves, then quarters, then eighths, and so on
• Subtraction – sing “Ten Green Bottles” while animating green bottles on a PowerPoint slide
• Percents – bring out a 25% off sale flyer for a department store, tell the children you’re going to buy a new outfit, but you’re not sure if you have enough money.
• Linear equations – dress as a plumber, carry a plunger or wrench. Tell students you have a tank to fill with water. It already holds 50 liters (/litres), and water is being added from a tap at 3.6 L per minute. How can we tell how much water there will be in the tank after an hour? How long will it take to reach 250 L? Could we graph the amount of water in the tank over time?

The actual idea isn’t that important; the main thing is to grab students’ interest, connect it with the math topic, and then while they’re paying attention, start teaching. It will require some time and effort put into preparation, but the payoff should be students who look forward to their next math lesson!

Photo by author.