Question

What does the probability of $1$ mean?

Answer 1

Probability is the chance that something will happen. The probability of an event is the likelihood of that event occurring. Probability is a value between (and including) zero and one. Probability is the branch of mathematics that deals with the likelihood of occurrence of an event.

Complete answer:
The probability of an event occurring is somewhere between impossible and certain. As well as words, we can use numbers to show the probability of something happening:
(1) Impossible is zero
(2) Certain is one

The probability of $1$ means the event is certain to happen, i.e. the event is a sure event.That means, the event will definitely occur. For example, the probability of getting a number greater than $0$ on throwing a die is $1$ since it is a sure event.

The probability of an impossible event is $0$. For example, the probability of getting a number greater than $6$ on throwing a die is $0$ since it is an impossible event. Also, the sum of all the probabilities of a random experiment is equal to $1$. The sum of probability of an event and its complementary event is $1$.

Note: If P(E) represents the probability of an event E, then $0$≤ P(E) ≤$1$. An event with a higher probability is more likely to occur than one with a lower probability. The probability of an event will not be less than $0$. This is because $0$ is impossible (sure that something will not happen). The probability of an event will not be more than $1$. This is because $1$ is certain that something will happen.