4 Ways of expressing probability

According to Equation 1, probability is defined as a fraction. However a fraction such as may also be expressed as a decimal number or as a percentage:

The following statements:

• the probability of event A is ,
• the probability of A occurring is 0.25,
• there is a 25% probability of the outcome being A,

are therefore all equivalent.

In addition, particularly in spoken language, it is common to say,

• there is a 1 in 4 probability of the outcome being A,

and that too is equivalent to the other three statements.

For the rest of this week probabilities will usually be expressed as fractions.

Now it is time to move on to probabilities that are related to more than one process.