**What is A Priori Probability?**

In Statistics, there are key concepts important to know that we can use in our everyday lives so that anytime an investor is about to make a decision, he can have a better approach to the reasoning process.

A priori Probability, from the Latin: (“from what is before”) is your best logical assessment of an outcome based on your current knowledge. It is different from **Priori Possibility.**

**Formula**

**Example:**

You through a fair dice and want to know the A Priori Probability of obtaining a 3 or a 4 or a 5 in a fair dice roll.

No. of desired outcomes: 3 (Roll a 3 or a 4 or a 5)

Total no. of outcomes = 6 (all equally likely possible outcomes of rolling a fair dice)

3 / 6 = .5 or 50%

Therefore, the probability of rolling a 3 or a 4 or a 5 in a fair dice roll is 50.0%

**Note:** the formula can only be used in cases when all the events are equally likely to occur and are mutually exclusive(where all events can’t occur at the same time). In the specific case of rolling fair dice, only one face of the dice can be on top, which makes this an exclusive event.

**Recommended Articles**

This article has been a guide to what is an A Priori Probability and its definition. Here we discussed the formula to calculate an a priori probability with examples and advantages, drawbacks, and differences. You can learn more about from the following articles:

**What is conditional probability?**

**What is an empirical probability?**

**What is a joint probability?**

**What is a joint probability?**

**What is a subjective probability?**