Probability can be written as a **fraction**.

On the top (numerator) of the fraction, we place the number of **options** we are looking for.

On the bottom (denominator) of the fraction, we place the total number of **possible combinations**.

**Example**

Look at these coloured cards.

What is the probability of selecting a red or blue card at random?

**Answer**

There are 2 options that we are looking for - the red and the blue card.

There are 6 possible combinations.

The probability of choosing a red or blue card is 2/6 which simplifies to **1/3**.

Having done that, what is the probability of choosing a yellow card?

There are 4 yellow cards out of a possible 6 cards, so the probability is 4/6 which simplifies to 2/3.

Can you see that the two answers of 1/3 and 2/3 add together to make the number 1? There is no other possible combination other than the ones we have looked at, so the total will be 1.

**The probability of something happening, plus the probability of it not happening will always equal 1.**

Let's have a go at some questions now.