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Basic Probability 

Classical Probability

Before you begin there are some key aspects of probability that you should keep in mind

  • A probability will always range from 0 to 1

  • The sum of probabilities for a given circumstance equals 1

 

PROBABILITY

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The classical approach to probability can be expressed with a fraction.

Prob Tri.PNG

Let’s say that we are randomly selecting shapes from a box

Box.PNG

In this box we have 3 different shapes and a total of 13 shapes. What would be my probability of randomly selecting a triangle?

Let’s use our fraction and tailor it to our specific situation

tri prob.PNG

In our box, we have a total of 3 triangles and 13 total shapes. Therefore,

prob tri solved.PNG

COMPLEMENTS 

The complement is the probability that something DOES NOT happen.

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Example:

What would the probability of NOT selecting a triangle be?

We can use our fraction format to figure this out

prob not tri.PNG

In our box, we have 10 shapes (5 squares and 5 circles) that are NOT triangles. Therefore,

prob not tri solved.PNG

Notice that  3/13 + 10/13 = 1. This is because, as stated before,  the sum of probabilities for a given circumstance equals 1.

Another way this could be solved is by subtracting the probability of selecting a triangle from 1. 

complement.PNG

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