To represent probabilities on the number line we will draw a horizontal or a vertical axis and mark the two numbers $0$ and $1$. The closer the probability mark is to zero, the lower the chance that a certain event will occur. The closer the probability mark is to one, the greater the chance that a certain event will occur.

Let's demonstrate this with an example

Inside a vase there are $7$ red balls and $7$ blue balls. We choose a ball from the vase at random.

We are asked to calculate what is the probability that we take a red ball out of the vase.

Let's start by drawing the number line and marking the numbers $0$ and $1$.

Let's look at the data we have.

In the vase there are $7$ red balls and $7$ blue balls, that is, in total there are $14$ balls.

We have a probability of $50$ percent of getting a red ball out of the vase, i.e. half, we will either get a red ball or we will not get a red ball (i.e. we will get a blue ball).

In other words, if we want to mark the probability of getting a red ball out of the vase we will do it exactly in the middle between $0$ and $1$, i.e. at $0.5$.

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