1. Independent events: Two events are said to be independent if the occurrence of one event does not affect the probability of the other event.
2. Mutually exclusive events: Two events are said to be mutually exclusive if they cannot occur at the same time.
3. Random variables: A random variable is a variable whose value is determined by chance.

Balaji considered the problem from first principles, the same way he taught hypothesis testing: state the null, gather evidence, decide. The null hypothesis: he would not create a PDF. The alternative: create a lawful, useful solution.

Balaji's Approach to Probability and Statistics