It took me so long to understand conditional probability.

Sal Rahman

But I finally got it.

The conditional probability of A given B is the ratio between the probability of both events A and B occurring together, and the probability of B occurring by itself.

Here's a concrete example.

Let's say you wanted to know what is the probability of drawing a heart from a deck of cards, given that you know that the card drawn is a red.

The conditional probability is defined as the ratio of the probability of drawing both a red and a heart, and just the probability of having picked heart.