Probability Line

Probability is the chance that something will happen. It can be shown on a line.

The probability of an event occurring is somewhere between impossible and certain.

As well as words we can use numbers (such as fractions or decimals) to show the probability of something happening:

  • Impossible is zero
  • Certain is one.

Here are some fractions on the probability line:

fraction probability line

We can also show the chance that something will happen:

a) The sun will rise tomorrow.
b) I will not have to learn mathematics at school.
c) If I flip a coin it will land heads up.
d) Choosing a red ball from a sack with 1 red ball and 3 green balls

probability of an event

Between 0 and 1

  • The probability of an event will not be less than 0.
    This is because 0 is impossible (sure that something will not happen).
  • The probability of an event will not be more than 1.
    This is because 1 is certain that something will happen.