Probability Properties

Probability Axioms

1.The probability is positive and less than or equal to 1.

0 ≤ p(A) ≤ 1

2. The probability of the sure event is 1.

p(S) = 1

3.If A and B are mutually exclusive, then:

p(A unión B) = p(A) + p(B)

Probability Properties

1 The sum of the probabilities of an event and its complementary is 1, so the probability of the complementary event is:

Probability of a Complementary Event

2 The probability of an impossible event is zero.

Probability of an Impossible Event

3 The probability of the union of two events is the sum of their probabilities minus the probability of their intersection.

Probability of the Union

4 If an event is a subset of another event, its probability is less than or equal to it.

Probability of an Event

5 If A1, A2, ..., Ak are mutually exclusive between them, then:

Probability of Mutually Exclusive Events

6 If the sample space S is finite and an event is S = {x1, x2, ..., xn} then:

Sample Space

For example, the probability of obtaining an even number, when rolling a die, is:

P(even) = P(2) + P(4) + P(6)