Probability Line

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

probability line

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

As well as words, we can use numbers to show the probability of something happening:

We can use fractions:

probability line fractions

Or percents:

probability line percents

Or decimals:

probability line decimal

Example: here we show the probability that:

probability line examples

  • 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 bag with 1 red ball and 3 green balls

Where would you place names like "fair chance", "remote chance", "possible", "probable" and "improbable"?

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.


People use many names when talking about probability! Such as odds, chance and so on.

Example: 50/50 chance

means exactly 50% chance, which is also 0.5 or ½


In mathematics we use the letter P to mean "probability of", like this:


Example: "the probability of choosing an ace is 1 in 13" is written:

P(ace) = 113

It sure saves a lot of writing!


703, 704, 705, 1478, 1479, 3812, 3813, 3814, 3815, 3816