Percentage selling poing

28th April 2006 at 01:00
Q) I teach a lower-ability maths group in Year10. Recently we have been revising percentages. I presented examples based on percentage reductions in sales prices. A couple of pupils work as part-time shop assistants in town. They asked me why they have to learn how to calculate percentages as where they work all the pricing is sorted out by the till. I pointed out that they might be the customer and want to compare prices across the different shops. Have you any examples I could discuss with them?

A) In some big department stores the sale price is not always displayed and there is just a "20% off" ticket. This is a great starter or ender for discussion - it's all in the language. Shops sometimes move items to a different location in the store and offer dramatic reductions - 70% off.

Recently I scoured the shelves of one shop and found an expensive brand of casserole dish with a knob missing from the lid. There were two sale labels attached. One said: "20% off. This product has been slightly damaged or shop soiled. A reduction of 20% will be offered at the till"; the other said: "50% off. This product has been damaged and is offered for sale at 50% off the lowest marked price." There was no original price written on the dish.

I approached the sales assistant to find out how much they were expecting me to pay. Before I go any further, perhaps you might like to work out the amount that you would expect to pay - the original price was pound;67. I would suggest displaying the picture on the board (email me if you would like the PowerPoint document).

Write "Original Price pound;67" and tell students that the sales assistant said the sale price was pound;33.50. Was she right?" Ask students to work in pairs to discuss the pricing. Feedback responses to the board.

Discuss with them how the store could avert confusion by clear labelling.

How would students have labelled the casserole for sale? It is difficult to write individual prices because of the large number of items involved.

Investigate the question: Is "70% off" the same as "20% then 50% off"? My argument ran as follows: the original price was reduced by 20%; 10% is Pounds 6.70 (pound;67 V 10), so 20% is pound;13.40 (2 X pound;6.70), so the first marked sales price was pound;53.60 (pound;67 - pound;13.40).

The second label states that there is 50% off the lowest marked price, that is pound;53.60. So pound;53.60 V 2 = pound;26.80, the argument being that the lowest marked price must be the previous sale offer.

If the store did not want this price to be quoted they should have taken the first label off. The amount is pound;6.70 less than the sales assistant wanted me to pay. In fact, a new knob costs pound;6.80 so it was well worth the effort!

I told the sales assistant that pound;33.50 was too much based on the labelling. She didn't agree so called over her sales supervisor, who also did not agree. Undeterred, I requested they consult the manager. Yes, I did get the dish for pound;26.80.

Q) What do you think of private tuition? I have been teaching for a couple of years. My degree and training left me with large debts and I thought private tuition might be a way to earn a bit extra.

A) When I started teaching my head of department gave me some very sound advice. He told me to wait until I had been teaching for a couple of years before becoming involved in tutoring. The reason wasn't about competence but about time commitments. He was right - the first year is exhausting and a steep learning curve. In the second year, I felt relaxed and able to contribute more to the department.

Having said that, private tuition can provide really good feedback into your mainstream teaching and it enables you to experiment with ideas. I know that this has, at times, led me to change my practice.

The internet now makes private tuition so much easier - no travelling needed; you can teach people from all over the world. I have been using a webcast collaborative e-solution, "i-teach", via a headset and webcam (broadband access needed). I can see and teach up to three tutees at a time. Lessons are uploaded as PowerPoint slides.

Interactive Flash animations, video clips and images can also be added at the click of a button. There is a whiteboard each participant can write on, which can also display PowerPoint images. The lessons can be saved and reviewed at a later date by tutee, parent and teacher.

* You can see archived lessons at

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