The video above is a commercially produced item - nice animation, Garage Band sound track, and it covers the basic facts well. Makes a change from me talking over PowerPoint slides!

I’ll add the question sheet on tree diagrams sometime on Monday.

The screencast above deals with

* The probability scale
* Expected frequency
* Bags of balls
* Mutually exclusive events
* Possibility space diagrams
* Independent events

A forthcoming sequel will talk you through tree diagrams. You need to have a recent version of the Flash Player installed to view videos from YouTube - try updating the Flash Player plug in on your Web browser if you have problems or just see a white square instead of the video.

Each brief explanation is introduced by a black slide with white text, use the scroll control to rapid wind through the screencast for the section you want to review.

You can download an MS Excel spreadsheet with probability simulations to go with the screencast. The spreadsheet simulates tossing a coin 100 times, and also simulates 100 repeats of tossing a coin 30 times to draw a chart.

Distance travelled is equal to the speed times the time taken. So if you drive at an average speed of 30 mph for two and a half hours, you will travel 75 miles. There are three permutations of the formula,

• Distance = Speed x Time
• Time = Distance divided by Speed
• Speed = Distance divided by Time

The formula triangle is often used to help remember these relationships. Just put your finger over the letter you are trying to find, and the triangle tells you what calculation to do for the remaining two letters.

Suppose you want to know the time a journey will take. Cover up T and the triangle reveals D / S or distance divided by the speed you drive at as the required calculation.

A quiz on decimal places, significant figures and rounding might help clarify this area of Number. Calculators give you 10 figures even when you want 3.

0.5 is the same as 50% is the same as a half. You need to know about fractions. Those nice people at the BBC Skillswise Web site have built a whole section on fractions, decimals and percentages. Go there!

I’ll be adding some worksheets and revision stuff on fractions here over the weekend.