Difference between revisions of "Probability"
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| − | For example, the probability of a tossed fair coin coming up heads is ½ = 0.5 = 50% because there is one | + | For example, the probability of a tossed fair coin coming up heads is ½ = 0.5 = 50% because there is one favorable outcome (heads) out of 2 possible outcomes (heads and tails). Another common example is standard deck of 52 playing cards: there are 13 cards in each suit: spades, hearts, clubs and diamonds. After the deck is shuffled thoroughly, the probability that the top card on the deck is a heart is <math>13 / 52 = 1 / 4 = 0.20</math>, or 20%. |
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Revision as of 20:12, June 12, 2009
The probability of an event is a number between 0 (representing impossibility) and 1 (representing certainty), and may be expressed as a simple fraction, decimal fraction, or percentage. When there are a finite number of equally likely outcomes, the probability of an event is given by
<math> \mbox{Prob}[\mbox{event}] =\frac{\mbox{number of favourable outcomes}}{\mbox{number of possible outcomes}} </math>.
For example, the probability of a tossed fair coin coming up heads is ½ = 0.5 = 50% because there is one favorable outcome (heads) out of 2 possible outcomes (heads and tails). Another common example is standard deck of 52 playing cards: there are 13 cards in each suit: spades, hearts, clubs and diamonds. After the deck is shuffled thoroughly, the probability that the top card on the deck is a heart is <math>13 / 52 = 1 / 4 = 0.20</math>, or 20%.