Probability: how big is the chance?
From impossible to certain: outcomes, chance as a fraction, decimal and percentage, and what happens when you throw many times. Read one step, play with it, then tap “I understand this”.
From impossible to certain
Probability measures how big the chance is that something happens. We use a scale from 0 (impossible) to 1 (certain). Halfway, at ½, is an even chance.
The marble bag
Change the marbles and see where the red arrow lands on the scale.
All the outcomes
An outcome is one possible result. First write down all the outcomes, then you can work out the chance.
What can happen?
Choose an experiment.
Chance as a fraction
Probability = favourable outcomes ÷ all outcomes. With 3 red out of 8 marbles, P(red) = 3 ÷ 8 = ⅜.
You can also write it as a decimal or a percentage: ⅜ = 0,375 = 37,5%. Use the marble bag in step 1 to practise.
Divide by all the outcomes, not by the other colour. 3 red and 5 blue is 3 out of 8, not 3 out of 5.
Every marble has the same chance of being pulled out. If 3 of the 8 are red, then in the long run you will pull out red about 3 times out of every 8.
Do the experiment
The chance tells us what we expect. What really happens differs a little. The more times you throw, the closer the results get to what you expect.
The dice machine
Throw 10 or 100 times and look at the bars.
Chance tells you what happens in the long run, not what happens next. A die has no memory: after three sixes, the chance of another 6 is still 16.
Play: what is the chance?
Chance game
Choose the right answer.
Correct: 0Check yourself
- Chance goes from 0 (impossible) to 1 (certain); ½ is an even chance.
- First write down all the possible outcomes.
- P = favourable outcomes ÷ all outcomes.
- The more times you do the experiment, the closer it gets to what you expect.
Write these points in your maths book. Read them again the night before the test.
Quick questions
Tap an answer. If you get one wrong, read why and go back to that step. You get new questions every time.
You ticked all 5 steps! Now you are ready for the quiz.- Practice sheet for this classQuestions + memo · 2 A4 pagesPractice sheet
- Data handling7 pages · PDFPaperMemo
Ready for more? The Grade 7 probability quiz gives you new questions every time.
- One step a day is enough. Ten calm minutes work better than an hour the night before the test.
- Play a board game with a die and keep track of how often each number comes up. Talk afterwards about what you expected.
- Ask your child to tell you the rule in their own words. If they can explain it, they understand it.
- The ticks (“I understand this”) are saved on this device only. We never ask for names or emails.
Follows CAPS for Grade 7 Maths. Always check your teacher’s notes and textbook too.