9.1 Probability scales
In real life, things usually fall somewhere in between the two extremes of ‘will never happen’ and ‘will definitely happen’.
We can use a probability scale to measure how likely events are to occur:
- The probability of an impossible event (‘will never happen’) is 0.
- The probability of a certain event (and ‘will definitely happen’) is 1.
- All other events come between 0 and 1.
- Events with an even chance have a probability of
.
Now try the following activity, where you’ll need a ruler and a pencil. Remember to check your answers once you have completed the questions.
Activity 15: Looking at probability
Use a ruler to draw your own probability scale. Mark on it 0, 1/2 and 1. Label 0 as ‘impossible’ and 1 as ‘certain’.
Then mark these statements on the probability scale with crosses and label them with their question letter:
- The probability that the sun will rise tomorrow.
- The probability that you will run the London Marathon next year.
- The probability of dying one day.
Answer
Here are the answers:
Of course, if you are a long-distance runner or plan to be one, your location for (b) might be closer to 1!
Summary
In this section you have:
- learned about the possibility of different events happening
- shown that some events are more likely to occur than others.
OpenLearn - Everyday maths 1
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