Math - Probability (Elementary Level)

Probability is the likelihood or the chance of an event happening. We use probability any time we want to know how likely something is to happen.


Probability can be expressed in 5 ways:

Equally Likely - we say this when there are equal chances for the events to happen.
          Ex. Suppose there are 4 pens in your case, 2 blue pens and 2 black pens. The chance of picking out a black pen is 2 out of 4. The same is true for the blue pen.

                                                           black pen = 2    blue pen = 2
                                      It is equally likely to get a black pen or a blue pen.

Likely - we say this when there is a higher chance for that event to happen.
          Ex. Suppose there are 5 pens in your case, 2 blue pens and 3 black pens. The chance of picking out a black pen is 3 out of 5. The chance for picking out a blue pen is 2 out of 5. Getting a black pen has a higher chance of happening.

                                                           black pen = 3    blue pen = 2
                                                One is likely to get a black pen than a blue pen.

Unlikely - we say this when there is a lower chance for that event to happen.
          Ex. Using the situation above, we see that the chance of getting a blue pen this time is lower.

                                                           black pen = 3    blue pen = 2
                                                          It is unlikely to get a blue pen.


Certain - we say this when there is a 100% chance of an event happening.
          Ex. Suppose you have 5 black pens in your case. What is the chance of picking out a black pen? It is certain.

Impossible - we say this when there is zero chance of an event happening.
          Ex. Using the situation above, what is the chance of picking out a blue pen? Since there are no blue pens here, there is zero chance of that happening. It is impossible.

Here are practice quizzes to learn more about probability:

Math 2 - Probability (Practice)
Here is a short practice on how to determine the probability of an event happening