Difference between revisions of "Probability"
m |
|||
| Line 1: | Line 1: | ||
| − | The '''probability''' of an event is a number between 0 (representing impossibility) | + | 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 |
| − | For example, | + | <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 favourable outcome (heads) out of 2 possible outcomes (heads and tails). | ||
With a 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 = 0.25</math>, or 25%. | With a 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 = 0.25</math>, or 25%. | ||
Revision as of 03:20, July 1, 2008
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 favourable outcome (heads) out of 2 possible outcomes (heads and tails).
With a 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 = 0.25</math>, or 25%.