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204 5.1 probability defns.

# 204 5.1 probability defns. - 5.1 Probabilities In every day...

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5.1 Probabilities In every day experience, terms such as almost certain or quite unlikely are often used. In science however we must be more precise in the terms. We would also like to be able to quantify statements. The quantification of the degree of certainty is the area of study called probability. You are already familiar with some probability. Since coin has 2 sides we say that the probability of getting heads on the flip of a fair coin is 0.5. Therefore, the probability of an event can be defined as the fraction of the total number of outcomes that will result in the event. More formally this concept can be defined as: Classical Definition of Probability If there are n equally likely outcomes of an experiment and an event E consists of s of these outcomes then the probability of E is s/n. For example, there are 52 cards in a deck, including 4 aces, thus we say the probability of drawing an ace from a deck is 4/52. Likewise, the probability of getting an even number of dots showing when we throw a fair die = 3/6 = 1/2. Frequency (Empirical) Definition of Probability Returning to the coin example, when we state that a fair coin will come up heads half the time we are saying that the probability of heads = 0.5.

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