Lecture 3: probability

In the last lecture on probability, there are two emphasis.

1. Mutually exclusive and independent events

2. Tree diagram

Mutually exclusive and independent events

It is important to differentiate these two types of events.

• Mutually exclusive events mean that they can never happen together.
• Independent events means that the happening of one event will not affect the probability of the other happening.
• Mutually exclusive events are NOT independent because if one event happens, the probability of the other happening drops to zero! (It does affect the probability of the other event happening.)
• It is very difficult to judge whether two events are independent based on your intuition. Please use the definition of independent events P( A intersect B) =P(A)P(B) to check whether two events are independent.

Tree diagram

• Tree diagrams are useful if

1. The event has a few stages

2. The outcome in one stage will affect the probability in the next stage.

By the end of the lecture, you can attempt tutorial 13.