Independent Events

Independent events have probabilities of occurring that don’t rely on each other.  For example, if I roll two dice, the number I get on the first die doesn’t affect what number I get on the second die.  They are independent events.  Another example is flipping several coins at once.  Say I get ‘heads’ on one coin.  Does this affect at all what I get for the other coins?  No!  So these events – the face I get on each coin – are all independent of each other.

We can use proper mathematical notation to define what must happen for two events to be independent:

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If we have two events, A and B, then this has to be true:


In English this means that if the two events are independent, I can calculate the probability of them both happening by simply multiplying the probabilities of each one happening by itself.