The idea, step by step
Chance describes what may happen
An impossible event cannot happen in the stated situation. A certain event must happen. Between these extremes, an event may be unlikely, equally likely with another, or likely. “Likely” does not mean guaranteed. Check the actual situation before choosing a word.
Use the available outcomes
In a mixed bag of five red balls and one blue ball, drawing red is more likely than drawing blue if every ball has the same chance of being chosen. Drawing a green ball is impossible because there are none. Drawing either red or blue is certain.
A common trap
A likely outcome must happen on the next trial.
Instead: A less likely outcome can still occur. Only a certain event is guaranteed.
See the thinking
A likely colour
A bag has five red balls and one blue ball. Which colour is more likely when one ball is drawn without looking?
- Every equal-sized ball has the same chance of being chosen.
- There are more red than blue balls.
Certain and impossible
A bag holds only yellow counters. Compare drawing yellow with drawing purple.
- Every available counter is yellow.
- No available counter is purple.
Check your understanding
A bag contains only red and blue balls. Is drawing green possible?
Show answer
No; it is impossible.
There is no green ball to choose.
Your turn
6 questions · 8 marks · Work at your own pace.
Read the questions online
- A bag contains four red balls and one blue ball. Which colour is more likely?1 mark
- A bag contains only green balls. Describe the chance of drawing a green ball.1 mark
- A bag contains only green balls. Describe the chance of drawing a red ball.1 mark
- A fair coin has a head and a tail. Compare the chances of the two outcomes.1 mark
- Order these from least to most likely: certain, impossible, likely, unlikely.2 marks
- A blue ball is unlikely to be drawn. Can it still be drawn on the next try? Explain.2 marks
Read the worked solutions
Equivalent correct methods earn the corresponding marks. Include units where asked.
- A bag contains four red balls and one blue ball. Which colour is more likely?1 mark
More of the equal-sized balls are red.
Red. - A bag contains only green balls. Describe the chance of drawing a green ball.1 mark
Every possible ball is green.
Certain. - A bag contains only green balls. Describe the chance of drawing a red ball.1 mark
There are no red balls.
Impossible. - A fair coin has a head and a tail. Compare the chances of the two outcomes.1 mark
A fair coin gives the two sides equal chances.
Equally likely. - Order these from least to most likely: certain, impossible, likely, unlikely.2 marks
Impossible and certain are the two extremes.
Impossible, unlikely, likely, certain. - A blue ball is unlikely to be drawn. Can it still be drawn on the next try? Explain.2 marks
It is not the same as impossible.
Yes. Unlikely still means possible.
Curriculum reference & lesson scope
Australian Curriculum v9 / SA Curriculum Mathematics 2026
Ordering likelihood; independent/dependent events; repeated trials; comparing variation.
Official curriculum source ↗