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 Coin
When a coin is tossed, there are two possible outcomes:
We say that the probability of the coin landing H is ½.
And the probability of the coin landing T is ½.
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 | Throwing Dice
When 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.
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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:
