Probabilities are written as FRACTIONS.

On the top of the fraction, we put the number of ways there are of your event happening.

On the bottom of the fraction, we put the total number of possible outcomes.

Reduce the fraction if you can.

Example

There are 3 red balls and 5 blue balls in a bag.

What is the probability of choosing a red ball?

Answer

On the top of the fraction, we put the number of ways there are of your event happening.  This will be the number of red balls (i.e. 3)

On the bottom of the fraction, we put the total number of possible outcomes.  This will be the total number of balls (3 + 5 = 8)

The probability is 3/8