Probability
How likely something is to happen.
Many events can't be predicted with total certainty. The best we can say is how likely they are to happen, using the idea of probability.Tossing a CoinWhen a coin is tossed, there are two possible outcomes:
And the probability of the coin landing T is ½. |
Throwing DiceWhen a single die is thrown, there are six possible outcomes: 1, 2, 3, 4, 5, 6.The probability of any one of them is 1/6. |
Probability
In general:Probability of an event happening = | Number of ways it can happen | |
Total number of outcomes |
Example: the chances of rolling a "4" with a die
Number of ways it can happen: 1 (there is only 1 face with a "4" on it)Total number of outcomes: 6 (there are 6 faces altogether)
So the probability = | 1 |
6 |
Example: there are 5 marbles in a bag: 4 are blue, and 1 is red. What is the probability that a blue marble will be picked?
Number of ways it can happen: 4 (there are 4 blues)Total number of outcomes: 5 (there are 5 marbles in total)
So the probability = | 4 | = 0.8 |
5 |
Probability Line
You can show probability on a Probability Line:
Probability is always between 0 and 1
Probability is Just a Guide
Probability does not tell us exactly what will happen, it is just a guideExample: toss a coin 100 times, how many Heads will come up?
Probability says that heads have a ½ chance, so we would expect 50 Heads.But when you actually try it out you might get 48 heads, or 55 heads ... or anything really, but in most cases it will be a number near 50.
Source: http://www.mathsisfun.com/data/probability.html
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