# 191. Fallen Revision

Which Maths teachers out there are fed up of stressing the same basic exam/test skills? Come on, there must be more than that? You there at the back. That’s more like it!

Unfortunately, us teachers don’t understand student basics:

* Pencils are for chewing, flicking or breaking.
* Rulers are for poking and twanging
* Working out is detrimental to doodling time
* And as for Units – wasn’t that mentioned in PSCHE to do with alcohol?

Sound familiar?

This term I’ve made my class reflect on the basics using a ‘Fallen Phrase’ puzzle template from Discovery Puzzlemaker. The skeleton of the phrase is given, but the missing letters are stacked at the bottom of each column – a bit like a collapsed ‘Wheel of fortune’ puzzle.

The puzzle covers all the basic skills, but it is difficult. My students had to really think what I nag them about, rather than just rearrange the letters.

I just hope all their hard work pays off in their test.

Visit the Discovery puzzlemaker site.

# 190. Visual Compound interest

So you’ve reached that bit of the Number curriculum at the end of Percentages – Simple and Compound interest. The theory is straight forward enough:

• Simple interest is calculated on the original balance.
• Compound interest is calculated fresh every year on the current balance.

This shouldn’t be a tricky concept, yet it is frequently  glossed over or partially taught to lower ability students. This is the maths they’ll need to get their head around at the bank in a few years time. So why not replace the scary calculations and rote learning with diagrams, which embed understanding.

Equipment

• Coloured pens
• Whiteboard
• Squared paper
• Ruler
• Calculator (Optional)

Simple Interest: Step 1

Draw a square which has sides which are a multiple of ten (I used 10×10). This area represents the original investment.

Step 2

Assume the interest rate is 10%. Calculate 10% of the area and shade it in lightly. Basically one column, since it’s a 10×10 grid.

Step 3

Add on 10% by drawing the shaded area again. This is the 1st interest payment.

Step 4

Repeat Step 3 for the 2nd and 3rd years.

Step 5

In summary, a simple interest (10%) investment over 3 years is the same as adding on 30%.

Compound Interest: Step 1

Repeat steps 1 -3 of simple interest

Step 2

Work out 10% of the height and draw a new row – since the grid is 10 squares high, it’s simply one square high.

Notice that the row is wider than the original square – the dotted area indicates the extra interest earned on the previous years interest. This starts the discussion that you are not adding on the same amount each time.

Step 3

Using the same concept as Step 2, work out 10% of the width of the diagram. This time the width is a little more than one square wide.

Once again it’s clear to see that you are adding on more than the last year.

Comparison: Simple vs Compound interest

Which is the better investment? It’s pretty clear to see:

You can compare these two types of interest using area calculations, rather than long lists of percentage calculations and you can actually ‘see’ the different methods.

# 189. Revision just flies by

I take absolutely no credit for this cute revision idea – japanese peace cranes for revision.

My class have a test next week and I gave them half an hour of directed independent study. Using their revision lists they could use their notes or textbooks to try questions or create a revision resource. I was expecting posters, maybe booklets … then one of the girls asked if could they make a crane for revision and hang off revision notes. Bearing in mind we have a 2m algebra tree in the room, I thought an industrial crane with notes hanging off it could be good.

How wrong I was!

Two girls started folding origami cranes – they’d learnt how for a school project. They then wrote maths facts on the wings. The idea was calmimg, yet contagious!

The idea slowly spread across the room. Soon about half the class were folding cranes and writing notes. Someone even found some coloured paper.

Now there is a small flock of cranes flying across the room which will hopefully remind pupils of the notes they wrote.

If you want instructions on how to fold an origami crane try this YouTube video.