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You are flipping a coin and wanting to find the probability of at least one head or at least one tail. Now it is clear that the probability of one coin flip landing heads is 1/2 and that of one coin flip landing tails is also 1/2. Now these two events are mutually exclusive as you cannot expect a coin land both heads and tails in one trial. Therefore you can determine the required

probability by the mere addition of the two probabilities : (or certainty).

Thus if A and B are two mutually exclusive events then the probability that either A or B will happen is the sum of the probabilities of A and B i.e. P (A + B) = P(A) + P(B)

Odds In Favor And Against

If P is the probability that an event will occur and q (= 1 - p) is the probability of the non-occurrence of the event; then we say that the odds in favor of the event occurring are p : q

(p to q) and the odds against its occurring are q : p.

For example, if the event consists of drawing a card if club from the deck of 52 cards, then the odds in favor are 

Similarly the odds against a card of diamond would be 3 : 1. The odds in favor of 4 or 6 in a
single toss of a fair die are ; i.e. 1 : 2 and the odds against are 2 : 1.

Multiplication Law of Probability

If there are two independent events; the respective probability of which are known, then the probability that both will happen is the product of the probabilities of their happening respectively P (AB) = P (A) ´ P (B)

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7. 1 Introduction
7.2 Trial
7.3 Sample Space
7. 4 Definition of Probability
7. 5 The Laws of Probability
7. 6 Conditional Probability
7. 7 Theoretical Distribution
7. 8 Binomial Distribution
7. 9 Normal Distribution
Chapter 8

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