PROBABILITY

# Probability

Let E the sample space of a random experiment and S the set of random events, then the **probability** is a function:

which verifies:

Properties:

Example: The result of a poll, done to Bachillerato students in a school, says that 40 % of them read a newspaper and 30 % read an information magazine. We know that 20 % read both of them, too. With these data, which is the probability that a randomly chosen student reads a newspaper or a magazine?

Let N = {read newspaper} and M = {read magazine}. The probabilities are:

P(N) = 0,4 P(M) = 0,3 P(N∩M) = 0,2

Then:

P(NUM) = P(N) + P(M) – P(N∩M)= 0,4 + 0,3 – 0,2 = 0,5

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