2.3 - What is Probability (Informally)?

We'll get to the more formal definition of probability soon, but let's think about probability just informally for a moment. How about this as an informal definition?

Probability
a number between 0 and 1
a number closer to 0 means "not likely"
a number closer to 1 means "quite likely"
If the probability of an event is exactly 0, then the event can't occur. If the probability of an event is exactly 1, then the event will definitely occur.

Try It! Section

Can you think of an event that cannot occur? Can you think of an event that will definitely occur?
An example of an event that can’t occur is rolling a seven from a fair six-sided die with face values {1, 2, 3, 4, 5, 6}. An example of an event that will definitely occur is the sun setting tonight.