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Everyday maths 1
Everyday maths 1

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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:

Described image
Figure 13 A probability scale
  • The probability of an impossible event (‘will never happen’) is 0.
  • The probability of a certain event (‘will definitely happen’) is 1.
  • All other events come between 0 and 1.
  • Events with an even chance have a probability of one divided by two.

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:

  • a.The probability that the sun will rise tomorrow.
  • b.The probability that you will run the London Marathon next year.
  • c.The probability of dying one day.


Here are the answers:

Described image
Figure 14 A probability scale (answer)

Of course, if you are a long-distance runner or plan to be one, your location for (b) might be closer to 1!


In this section you have:

  • learned about the possibility of different events happening
  • shown that some events are more likely to occur than others.