Describing probabilities and the probability scale

Describing probabilities

We often make judgements as to whether an event will take place, and use words to describe how probable that event is. For example, we might say that it is likely to rain tomorrow, or that it is impossible to find somebody who is more than \({3}~{m}\) tall.

Other commonly used words to describe the chance of an event happening include:

  • certain
  • very likely
  • even chance
  • unlikely
  • very unlikely

The probability scale

Maths uses numbers to describe probabilities. Probabilities can be written as fractions, decimals or percentages. You can also use a probability scale, starting at \({0}\) (impossible) and ending at \({1}\) (certain).

Here are some events placed on the probability scale.

Scale showing probability of events happening. The scale includes specific events that have different probabilities of happening including 1 (certain), ½ (even) and 0 (impossible).

Have a look at ordering the probabilities in the question below.