By the end of this lesson the student will:

• analyse experiments to determine the theoretical probability of events
  
  
• carry out experiments involving chance to estimate the probability of events and to simulate situations
  
  
• interpret and evaluate information contained in tables, visual displays and databases and report on methods of data collection
  
  
• draw inferences from collected or published data.

There are long-term events that happen year after year and affect the rainfall pattern. The Bureau of Meteorology analyses the past patterns and tries to predict the future patterns. The predictions are presented as probabilities (chances) and published to help people make informed decisions.

The three wheels (pie charts) you'll see on the website given in the Resources section below tell you what the chance of rain is during different climatic events.

In an El Niño climate event, there is a greater chance of low rainfall and a smaller chance of high rainfall. In a La Niña climate event, there is a greater chance of high rainfall and smaller chance of low rainfall.

Knowing when it is more likely to rain helps farmers to plan ahead and reduce the risk of a bad year.

You'll need to access the content at the following internet location : (clicking on the following link will cause a 300K animation to download)Different Amounts of Rain at Different Times. If the internet is not available to students, print off this lesson plan and worksheet, and have the students cut out pie charts and make tops for use in the activity. For tops you'll need toothpicks, scissors and prints of the pie charts (see worksheet).

Print off the student's worksheet and photocopy one for each student.

Southern Oscillation Index (SOI) definition.

Print off the SOI graph and the SOI monthly values for reference material. Make photocopies for students who don't have internet access.

Ask the students to carry out the activity from the worksheet then go over their results at the end of the class.

Solutions

1. Student's answers will vary. Some student's may not record one letter after another. To have the letters presented in one long sequence will help in getting across the fact that each spin is an independent event. Some student's may get quite a few D's in a row, which they may not have expected.
   
   
2. Student's answers will vary. The totals of each of the three states should be multiplied by 2 to convert to percentage figures.
   
   
3. The results should be very close or even the same.
   
   
4. Spin the pie charts 100 times to make it easier to come up with percentages.
   
   
5. The chance of Red landing on the pointer is 25%
   The chance of Blue landing on the pointer is 25%
   The chance of Green landing on the pointer is 25%
   The chance of Yellow landing on the pointer is 25%
   
   
6. The answer will depend on the SOI values presented at the time.
   
   
7. The answer will depend on the SOI values presented at the time.
   
   
8. Student's answers will vary. The bar graph is easier to read and allows you to detect an El Niño episode much quicker than the monthly values. The monthly values gives exact figures. To improve the monthly values the monthly columns could be labelled along the bottom as well as the top. Guidelines could be used on the bar graph to make it easier to associate the bar with the month.
   
   
9. I expect to get a score of 15 Wet, 5 Dry and 10 Normal out of 30 spins.
   
   
10. The student's answers will vary.
    
    
11. The result of each spin is independent of the result of the previous spin. The expected results are based on theory while the actual results are due to chance. Just because there is a 50% chance that Normal will come up doesn't mean that it will definitely come up for 50% of the total spins.
    
    
12. Student's answers will depend on the SOI values presented at the time.