There is a mistake in the tutorial about conditional probability! Please read this note carefully and make adjustments.
The conditional probability of an event B in relationship to an event A is the probability that event B occurs given that event A has already occurred. The notation for conditional probability is P(B|A), read as the "probability of B given A". The formula for conditional probability is:
P(B|A) = P(A and B) / P(A)
Source: Created by Emily LeBlanc-Perrone using Brase & Brase Understandable Statistics